# Glossary

<AlphaToolbar letters={["7","A","B","C","D","E","F","G","I","J","L","M","N","O","P","R","S","T","U","V","W"]} />

## 7

### [7-bit Encoding](/docs/glossary/what-is-7-bit-encoding)

7-bit encoding is the same as Ascii encoding: both represent alphanumeric characters and symbols as numbers.

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## A

### [A Record](/docs/glossary/what-is-an-a-record)

An A Record — more accurately, a ‘DNS A Record' — links a domain to an IP address.

### [Account Notifications](/docs/glossary/account-notifications)

Account Notifications are timely, relevant, and personalized messages sent by companies to their customers about their accounts.

### [Ahoy](/docs/glossary/what-is-ahoy)

Ahoy, a signal word originally used to call a ship, was once a standard way to greet others and was Alexander Graham Bell's suggested greeting for answering the telephone.

### [Alphanumeric Sender ID](/docs/glossary/what-alphanumeric-sender-id)

An Alphanumeric Sender ID is your company name or brand used as the Sender ID in one-way SMS messages sent to supported countries. Alphanumeric Sender IDs may be up to 11 characters long. Accepted characters include both upper- and lower-case Ascii letters, the digits 0 through 9, and the space character. They may not be only numerals.

### [API](/docs/glossary/what-is-an-api)

An Application Programming Interface (API) is provided by a service owner so that others may use the features and functions enabled by the service. APIs describe how a consumer will make requests of the service, and what they will receive in return.

### [API Key](/docs/glossary/what-is-an-api-key)

An Application Programming Interface (API) Key is a unique identifier that is used to authenticate a developer or program to an API.

### [Application](/docs/glossary/what-is-an-application)

An Application, often shortened to 'app', is a program, or set of programs, that allows end-users to perform particular functions. For example, ecommerce companies provide applications to customers to facilitate purchases and service.

### [Application-to-Person Messaging](/docs/glossary/what-a2p-sms-application-person-messaging)

Application-to-Person messaging (A2P) is any kind of message traffic in which a person is receiving messages from an application rather than another individual, and which is not expected to receive a reply. A2P message includes, but is not limited to, marketing communications, appointment reminders, chatbots, notifications, and one-time passwords (OTPs) or PIN codes.

### [Appointment Reminder](/docs/glossary/what-is-an-appointment-reminder)

An Appointment Reminder is a message sent by a business to notify a customer of an upcoming event, such as an eye test, a restaurant booking or a package delivery. While some businesses call customers to remind them of their appointments, text messaging has emerged as the preferred channel for this kind of communication.

### [Area Code Overlay](/docs/glossary/what-area-code-overlay)

An Area Code Overlay is an area code that covers the same geographical space as another area code. In North America, each area code has a potential capacity of around 8 million unique phone numbers — 7,919,900, to be exact. Many area codes have exhausted all possible phone numbers, so one or more area codes are added to accommodate.

### [Arrival Alerts](/docs/glossary/what-are-arrival-alerts)

An Arrival Alert is sent by a business to inform one of its customers when they might expect their product or service to arrive.

### [Artificial Intelligence](/docs/glossary/what-is-artificial-intelligence)

Artificial Intelligence (AI) is the ability of a computer to mimic human cognitive skills, such as learning and understanding.

### [Attribute-Based Routing](/docs/glossary/what-is-attribute-based-routing)

Attribute-Based Routing is a process used by contact center applications to distribute tasks according to a set of defined characteristics.

### [Authentication Token](/docs/glossary/what-is-an-authentication-token)

An Authentication Token (auth token) is a piece of information that verifies the identity of a user to a website, server, or anyone requesting verification of the user's identity.

### [Autonomous Agents](/docs/glossary/what-are-autonomous-agents)

Autonomous Agents are artificial intelligence (AI) systems that can perform a series of complex tasks entirely undirected to achieve a goal. An autonomous agent needs to reason, plan and interact with the necessary systems and real world to solve a problem.

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## B

### [Basic Authentication](/docs/glossary/what-is-basic-authentication)

Basic Authentication is a method for an HTTP user agent (e.g., a web browser) to provide a username and password when making a request.

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## C

### [C#](/docs/glossary/what-is-csharp)

C# — pronounced "see sharp" — is an object-oriented and statically typed computer programming language created by Microsoft for use on its .NET platform. Its name comes from the C language, from which it inherits a similar syntax.

### [Call Attribution](/docs/glossary/what-is-call-attribution)

Call Attribution is a way to track calls by tying phone numbers to data from an ad source, such as keywords, sessions or campaigns. It provides visibility into digital campaigns and allows accurate measurement of marketing return on investment (RoI).

### [Call Center](/docs/glossary/what-is-a-call-center)

A call center is the heart of customer service for many businesses, where customers call in for help and reps call out for sales. It's referred to as a call center because traditional models of customer service are based on phone support as the main method of contact between customers and companies. A modern call center is often referred to as a contact center.

### [Call Routing](/docs/glossary/what-is-call-routing)

Call routing refers to the procedure of sending voice calls to a specific queue based on predetermined criteria. A call routing system is also known as an automatic call distributor (ACD).

### [Call Tracking](/docs/glossary/what-is-call-tracking)

Call Tracking is a software-based performance marketing technique that generates and assigns a unique phone number to a specific advertisement or marketing campaign. Call Tracking systems then follow and analyze leads through that phone number channel to understand the channel's true effectiveness and ROI or receive a commission for driving that lead.

### [Call Transcription](/docs/glossary/what-is-call-transcription)

Call transcription is the conversion of a voice or video call audio track into written words to be stored as plain text in a conversational language. Call transcription can either be live - as a call or event happens - or based on the recording of a past conversation.

### [Call whisper](/docs/glossary/call-whisper)

Call Whisper, also commonly referred to as Call Screening, involves playing a message to the callee while the caller continues to hear ringing. It can provide additional information such as the source or purpose of the call to the callee before the call begins and even allow the callee to accept or reject the call based on that information.

### [Chatbot](/docs/glossary/what-is-chatbot)

A chatbot is an artificial intelligence (AI) program that creates conversational interaction between the chatbot and another user through voice commands or text chats.

### [Click-to-Call](/docs/glossary/what-is-click-to-call)

Click-to-call, sometimes called click-to-talk or click-to-dial, is a way to let people connect with a company representative by phone while they're browsing a website or in an app.

### [Cloud Contact Center](/docs/glossary/what-is-a-cloud-contact-center)

Cloud contact centers make contact center software functionality that was previously only accessible through on-premise hardware available through the internet. A cloud contact center provides quick and easy access to the tools and services businesses need to communicate in today's web-based world.

### [Contact Center](/docs/glossary/what-is-a-contact-center)

A contact center is a business's central point for managing all customer communications across all channels. A company's contact center is usually integrated with their customer relationship management (CRM) system, where all interactions between the organization and the public are tracked, coordinated, and managed.

### [CPS](/docs/glossary/cps)

Calls per second

### [Customer Engagement](/docs/glossary/what-is-customer-engagement)

Customer engagement is the emotional connection between your company and your customers, sentiments which strongly influence their buying decisions. Customers who actively engage with a business tend to be more loyal and spend their money supporting brands they feel connected to.

### [Customer Experience](/docs/glossary/what-is-customer-experience)

Customer experience (CX) refers to the interactions between a customer and an organization throughout all points of contact along the customer journey. Based on this customer experience definition, customer loyalty and company revenue growth will naturally follow positive interactions with your brand.

### [Customer Journey](/docs/glossary/what-is-a-customer-journey)

A customer journey is the total sum of experiences a customer has when interacting with a business or organization. Rather than focusing on a specific interaction, the customer journey takes all points of contact into account.

### [Customer Relationship Management (CRM)](/docs/glossary/what-is-customer-relationship-management)

Customer relationship management, usually referred to as CRM, is a method for managing an organization's relationships with its customers. Most often, the term CRM refers to a CRM system—which is software for managing contacts, streamlining sales processes, and improving business relationships.

### [Customer Satisfaction Score (CSAT)](/docs/glossary/what-is-a-csat-score)

Short for Customer Satisfaction Score, CSAT is a measurement to determine whether a customer feels their expectations have been fulfilled by a company's products and services.

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## D

### [Deliverability Score](/docs/glossary/deliverability-score)

Get an overview of how your Twilio messaging traffic is performing with your Deliverability Score.

### [Direct Inward Dialing (DID)](/docs/glossary/what-direct-inward-dialing-did)

Direct Inward Dialing (DID) is a telephone service that allows a phone number to ring through directly to a specific phone at a business instead of going to a menu or a queue and needing to dial an extension. A phone number that is used like this is often called a "DID" (and multiple numbers are called "DIDs").

### [DTMF Tones (Dual-Tone Multi-Frequency Tones)](/docs/glossary/what-is-dtmf)

DTMF, or Dual-Tone Multi-Frequency tones, are in-band telecommunications signals sent over voice frequencies.  Commonly used over telephone lines, DTMF tones are also commonly called Touch Tones.

### [Dynamic Number Insertion (DNI)](/docs/glossary/what-is-dynamic-number-insertion)

Dynamic Number Insertion (DNI) is a call tracking feature where a unique phone number is tied to each ad source. This helps marketers analyze offline behavior much in the same way they track online behavior with the help of cookies.

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## E

### [E.164](/docs/glossary/what-e164)

E.164 is the international telephone numbering plan that ensures each device on the PSTN has a globally unique number.
This numbering plan allows phone calls and text messages to be correctly routed to individual phones in different countries. E.164 numbers are formatted as `+` `country code` `subscriber number including area code` and can have a maximum of fifteen digits.

### [ETA Alerts](/docs/glossary/what-are-eta-alerts-estimated-time-of-arrival)

ETA Alerts, or Estimated Time of Arrival Alerts, are periodic notifications on the status of an item, delivery, or person that include a probable time of arrival at the destination.  Usually delivered through SMS messages or voice calls, ETA alerts keep customers updated on the location and timing of their upcoming deliveries.

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## F

### [Flex Dialpad](/docs/glossary/what-is-flex-dialpad)

The Flex Dialpad is a native feature of the Flex UI v1.18.0 and above which offers all of the theming and customizability features of a React component.
Flex Dialpad allows agents to make outbound calls to customers directly from the UI and real-time and historical reporting through Flex Insights.
With the programmable Flex Dialpad, developers can build click-to-dial use cases via the new Action Framework action, startOutboundCall. For instance, you can program the Dialpad in such a way that Flex retrieves contact data from your business application and subsequently present it to an agent. This kind of automation avoids any possible risk of misdialing and reduces time-to-call by leveraging data that resides in your application.

### [Flex Insights](/docs/glossary/what-is-flex-insights)

Flex Insights allows you to perform workforce optimization (WFO) in Twilio Flex. It provides a 360-degree view of every conversation in your Flex contact center so that you can provide agents with valuable feedback, knowledge, and skills.

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## G

### [General Data Protection Regulation (GDPR)](/docs/glossary/what-general-data-protection-regulation-gdpr)

The General Data Protection Regulation (GDPR) of the European Union (EU) is a law that regulates the handling of personal data and outlines the rights individuals have with regard to their data. It was implemented on May 25, 2018. It applies to any <a href="https://ec.europa.eu/info/law/law-topic/data-protection/reform/what-does-general-data-protection-regulation-gdpr-govern_en">"individual, company, or organization"</a> that processes the data of a person in the EU. This applies whether the organization is based in the EU or elsewhere.

### [General Packet Radio Service (GPRS)](/docs/glossary/what-general-packet-radio-service-gprs)

GPRS, or General Packet Radio Service, is a best-effort packet-switching communications protocol for cellular networks.  
GPRS was one of the first widely used data transfer protocols on cellular networks, first standardized in began to support GPRS in 2000.

### [GSM-7](/docs/glossary/what-is-gsm-7-character-encoding)

GSM-7 is a character encoding standard which packs the most commonly used letters and symbols in many languages into 7 bits each for usage on GSM networks.  As SMS messages are transmitted 140 8-bit octets at a time, GSM-7 encoded SMS messages can carry up to 160 characters.

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## I

### [Interactive Voice Response (IVR)](/docs/glossary/what-is-ivr)

Interactive voice response (IVR), also known as a phone tree, provides an automated telephony system for callers using voice and touch-tones (DTMF).

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## J

### [Jitter](/docs/glossary/what-is-jitter)

Jitter is the variation in periodicity of a signal or periodic event from its target or true frequency.  In telecommunications, jitter further refers to the variation in latency of packets carrying voice or video data over a communications channel.

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## L

### [Large Language Model (LLM)](/docs/glossary/what-is-a-large-language-model)

Large Language Models or LLMs are artificial intelligence models that can generate and process human-like text. Some popular LLMs include OpenAI's GPT-4, Google's Gemini and Meta's Llama 2.

### [Latency](/docs/glossary/what-is-latency)

Latency is the time delay between the initiation of an event and its perception by some observer.  In networking and telecommunications, latency is the time between a sender causing a change in a system's state and its reception by an observer.  Network latency is often informally used interchangeably with lag.

### [Live Chat](/docs/glossary/what-is-live-chat)

Live chat is a type of online chat distinguished by its simplicity and user accessibility. Live chat appears in a web browser or in mobile applications, usually via a small pop-up modal through which the visitor can exchange text messages with a chat operator in real time.

### [Long Code](/docs/glossary/what-long-code-phone-number)

A long code number is a standard phone number used to send and receive voice calls and SMS messages. Phone numbers are typically called "long codes" (10-digit numbers in many countries) when comparing them with SMS short codes (5-6 digit numbers).

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## M

### [Machine Learning](/docs/glossary/what-is-machine-learning)

Machine learning is an application of artificial intelligence that enables computer programs to learn and improve automatically as they are exposed to new data, without being explicitly programmed.

### [Masked Calling](/docs/glossary/what-is-masked-calling)

Masked Calling is a technique used in ecommerce to protect buyers' and sellers' personal phone numbers. Each party gets a temporary number, allowing them to communicate for a specified time period. When the time period expires, the numbers are recycled and reassigned to other parties on the platform. This prevents transactions from happening outside the platform. 

### [Masked Phone Numbers](/docs/glossary/what-are-masked-phone-numbers)

Masked Phone Numbers are a common pattern to anonymize communication between multiple parties and hide participant phone numbers. Instead of dialing directly from phone to phone, users communicate via a third ('proxy') phone number that forwards a call to the eventual destination. 

### [Mean Opinion Score (MOS)](/docs/glossary/what-is-mean-opinion-score-mos)

A Mean Opinion Score (MOS) is a numerical measure of the human-judged overall quality of an event or experience.  In telecommunications, a Mean Opinion Score is a ranking of the quality of voice and video sessions.
Most often judged on a scale of 1 (bad) to 5 (excellent), Mean Opinion Scores are the average of a number of other human-scored individual parameters.  Although originally Mean Opinion Scores were derived from surveys of expert observers, today a MOS is often produced by an Objective Measurement Method approximating a human ranking.

### [Messaging Character Limits](/docs/glossary/what-sms-character-limit)

A single SMS message technically supports up to 160 characters, or up to 70 if the message contains one or more Unicode characters (such as emoji or Chinese characters).
However, modern phones and mobile networks support message concatenation, which enables longer messages to be sent. Messages longer than 160 characters are automatically split into parts (called "segments") and then re-assembled when they are received. Message concatenation allows you to send long SMS messages, but this increases your per-message cost, because SMS are billed per segment.
The 160-character limit is for messages encoded using the GSM-7 character set. Messages not encoded with GSM-7 are limited to 70 characters. For detail on how these character limits change on concatenated (multi-segment) messages, see below.
Twilio's platform supports long messages up to 1600 characters across all Programmable Messaging channels, including SMS and RCS. However, for SMS messaging, Twilio recommends sending messages that are no more than 320 characters to ensure the best deliverability and user experience.\
RCS supports a more size-efficient character encoding scheme called UTF-8.  With UTF-8, Unicode characters are natively supported and take up less character-length space that would otherwise lead to higher segment counts over SMS.

### [Microprocessor](/docs/glossary/what-is-a-microprocessor)

A Microprocessor is an integrated circuit whose function is almost infinitely changeable through programming.

### [MMS](/docs/glossary/what-is-mms)

MMS, short for Multimedia Messaging Service, is a standard way to send multimedia such as pictures, videos, and other attachments over text messaging channels.

### [Multichannel](/docs/glossary/what-is-multichannel)

In a multichannel contact center, companies connect with customers via multiple communications channels – such as email, social media, web chat, and voice. However, just because customers connect via multiple channels does not mean that their experience is seamless.

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## N

### [National Format](/docs/glossary/national-format)

Twilio's Lookup API returns phone numbers in national format, a string containing the phone number formatted according to the most common style in the associated country.

### [Natural Language Processing (NLP)](/docs/glossary/what-natural-language-processing-nlp)

Natural language processing (NLP) describes the methods computers use to parse human speech. It's been a branch of research in linguistics, computer science, and artificial intelligence (AI) for many decades. In what follows, we'll explore what NLP is and discuss some of its applications.

### [Natural Language Understanding (NLU)](/docs/glossary/what-is-natural-language-understanding)

Natural language understanding (NLU) uses the power of machine learning to convert speech to text and analyze its intent during any interaction.

### [Net Promoter Score (NPS)](/docs/glossary/what-is-net-promoter-score)

Net promoter score, often referred to as NPS, is an important metric that measures how likely customers are to recommend a business. The idea behind NPS is companies who are recommended by their customers are more likely to grow.

### [Network Address Translation (NAT)](/docs/glossary/what-is-network-address-translation-nat)

Network Address Translation (NAT) is the modification of in-transit network packets to map one IP address space to another.  It is most commonly used in IP Masquerading, where a large private IP network shares a relatively small number of publicly facing IP addresses behind a router or gateway.

### [Network Edge](/docs/glossary/what-is-a-network-edge)

A network edge is a location where a computer network interfaces with the Internet. A network connected to the Internet may have one or more network edges located in data centers throughout the world.

### [North American Area Codes](/docs/glossary/north-american-area-codes)

North American Area Codes are prefixed to a phone number to assist in routing phone calls in North America. The North American Numbering Plan (NANP) dictates the regional and non-geographic area codes assigned to signatory countries. The United States, Canada, some Caribbean countries, and all US territories are covered by the plan.

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## O

### [Omnichannel Contact Center](/docs/glossary/what-is-omnichannel)

In an omnichannel contact center, all communication channels (e.g., phone, SMS, online chat, and email) connect and integrate to provide a seamless customer experience. Omnichannel contact centers also let agents switch between channels with a single user interface without losing context from customer interactions across channels.

### [On-Premise Contact Center](/docs/glossary/what-is-an-on-premise-contact-center)

An on-premise contact center is a model where the customer houses all the required software and hardware. Companies that use an on-premise system generally employ or contract specialized IT staff to configure, upgrade, and maintain the contact center.

### [Order notifications](/docs/glossary/order-notifications)

Order notifications give businesses the ability to inform customers of the status of their order, which could include confirmations, pricing adjustments, delays in fulfillment, or delivery scheduling.

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## P

### [P2P SMS](/docs/glossary/what-p2p-sms-person-person-messaging)

P2P stands for Person-to-Person messaging. In simple terms, this is when two or more people communicate over text messaging. For example, when you send a text message from your phone to another person's phone, that's P2P. Under some circumstances, this may also include traffic that goes through an API to connect two people, however some countries (including the US and Canada) do not consider any application-mediated traffic to be P2P.

### [Packet Loss](/docs/glossary/what-is-packet-loss)

Packet loss refers to the failure of packets to reach their destination on a network.  Packet loss is most often a consequence of network congestion and usually caused by network equipment dropping, ignoring, misdelivering, or discarding packets.

### [PDD](/docs/glossary/what-is-post-dial-delay)

Post-dial delay (PDD) is the measurement of how long it takes for a calling party to hear a ringback tone after initiating a call. Technically it is the delta between the SIP INVITE and a 180 Ringing or 183 Session Progress response. 

### [Personally Identifiable Information (PII)](/docs/glossary/what-is-personally-identifiable-information-pii)

Personally Identifiable Information (PII), or personal data, is data that corresponds to a single person. PII might be a phone number, national ID number, email address, or any data that can be used, either on its own or with any other information, to contact, identify, or locate a person.

### [Phone Menu](/docs/glossary/what-is-a-phone-menu)

A phone tree or phone menu is an automated navigation menu presented to voice callers. Using interactive voice response with DTMF codes (touch tones) or voice recognition, a phone menu helps a caller find automated information, complete a transaction, talk to the proper human operator, or leave a voicemail with a company.

### [Platform](/docs/glossary/what-is-a-platform)

A platform is any combination of hardware and software used as a foundation upon which applications, services, processes, or other technologies are built, hosted, and/or run. Platforms offer the ability to build within an existing technical framework, decreasing both development time and cost.

### [Private Branch Exchange (PBX)](/docs/glossary/what-is-pbx-private-branch-exchange)

PBX, short for Private Branch Exchange, is a phone system in an enterprise that manages incoming and outgoing phone calls as well as an organization's internal communications.

### [PSTN (Public Switched Telephone Network)](/docs/glossary/what-is-pstn)

The PSTN (Publicly Switched Telephone Network) is the network that carries your voice calls when you call from a landline or cell phone. It refers to the worldwide network of voice-carrying telephone infrastructure, including privately-owned and government-owned infrastructure.

### [Push Notification](/docs/glossary/what-is-push-notification)

A push notification (also known as a server push notification) is the delivery of information to a computing device from an application server where the request for the transaction is initiated by the server rather than by an explicit request from the client. While 'push notification' is most often used to refer to notifications on mobile devices, web applications also leverage this technology.

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## R

### [React](/docs/glossary/what-is-react)

React (or sometimes ReactJS) is a JavaScript library for building user interfaces. It's sometimes also referred to as a framework.
 
The library focuses on creating declarative UIs using a component-based concept. Although React is often connected to front-end JavaScript development it can also be used to render views server-side in React Native. While React is open source, it is mainly developed by Facebook.

### [REST API](/docs/glossary/what-is-a-rest-api)

A REST API allows software programs to expose functionality and data to other programs over the Internet in a consistent format. APIs are considered RESTful if the means of accessing the API provider's functionality adhere to the architectural style of REST.

### [Retrieval-Augmented Generation (RAG)](/docs/glossary/what-is-retrieval-augmented-generation)

Retrieval-augmented generation is a technique in which relevant  content (typically text) gets retrieved and pre-processed to  augment the prompt that gets passed to a Large Language Model  to provide additional knowledge and improve accuracy.

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## S

### [SDK](/docs/glossary/what-is-an-sdk)

A software development kit, or SDK, is a downloadable software package that contains the tools you need to build on a platform.

### [Sentiment Analysis](/docs/glossary/what-is-sentiment-analysis)

Sentiment Analysis, or opinion mining, is the process of determining whether language reflects positive, negative, or neutral sentiment. Using sentiment algorithms, developers and brand managers can gain insights into customer opinions about a topic.

### [Serverless Architecture](/docs/glossary/what-is-serverless-architecture)

Serverless architecture (also known as serverless computing or function as a service, FaaS) is a software design pattern where applications are hosted by a third-party service, eliminating the need for server software and hardware management by the developer. Applications are broken up into individual functions that can be invoked and scaled individually.

### [Session Initiation Protocol (SIP)](/docs/glossary/what-is-session-initiation-protocol-sip)

Session Initiation Protocol (SIP) is a signalling protocol for initiating, terminating, and modifying user sessions over an IP network.  Most commonly, SIP is used for Voice Over IP (VoIP) services, but is also often used for other communications sessions such as video calls and instant messaging sessions.

### [Short Code](/docs/glossary/what-is-a-short-code)

Multiple countries support numbers for text messaging that have fewer digits than typical phone numbers.

### [SIM](/docs/glossary/sim)

The acronym SIM stands for Subscriber Identification Module. A SIM is used to authorize a subscriber to access a mobile network. SIMs can come in many form-factors, including cards and chips.

### [SIP INVITEs](/docs/glossary/sip-invites)

A SIP INVITE is a SIP request message that initiates a SIP call. 
 
A SIP INVITE is made up of lines of text. The first line in an INVITE is called a Request-Line, which is followed by more lines of text called headers. The headers contain information about the INVITE, such as the identity of the caller, whether the INVITE was forwarded before being sent to the recipient, and the number of times a call may be forwarded. 

### [SIP Trunking](/docs/glossary/what-is-sip-trunking)

What is SIP Calling?
SIP (Session Initiation Protocol) trunking refers to phone calls that are routed over the Internet rather than traditional phone lines. SIP calling, therefore, refers to the act of placing calls via a SIP trunk. Because SIP calls take place across the Internet, they tend to be cheaper and more efficient than calls placed through traditional phone systems.
Physical connections to a phone company are eliminated with the use of a SIP trunk. Using SIP trunks, a SIP provider can connect multiple channels to your private branch exchange (Voice-over-IP (VoIP) infrastructure.

### [SMS](/docs/glossary/what-is-an-sms-short-message-service)

SMS stands for Short Message Service and is another name for a text message. An SMS is generally sent from one mobile device to another over the cellular network. SMS is a text-only standard first formalized in 1985 in the Global System for Mobile Communications (GSM) standards.

### [SMS API](/docs/glossary/what-is-sms-api-short-messaging-service)

A SMS API is well-defined software interface which enables code to send SMS Gateway.
As the infrastructures for SMS communications and the internet are mostly divided, SMS APIs are often used to 'bridge the gap' between telecommunications carrier networks and the wider web.  SMS APIs are used to allow web applications to send and receive text messages through logic written for standard web frameworks.

### [SMS Delivery](/docs/glossary/what-is-sms-delivery-deliverability)

SMS Delivery is a measure of the percentage of outgoing SMS and MMS messages which are received at their intended destination.  While sometimes referring to the status of a single message, SMS delivery usually is a rate of delivered versus intended messages and summarized as an 'SMS Delivery Rate.'

### [SMS Gateway](/docs/glossary/what-is-a-sms-gateway)

An SMS Gateway enables a computer to send and receive SMS text messages to and from a SMS capable device over the global telecommunications network (normally to a mobile phone). The SMS Gateway translates the message sent, and makes it compatible for delivery over the network to be able to reach the recipient.

### [SMS Notifications](/docs/glossary/what-are-sms-notifications)

SMS Notifications are out-of-band text messages sent in response to events or transactions which occur somewhere else. While often used as a marketing tool to increase the percentage of returning visitors, SMS notifications are very useful for organization and public safety purposes as well.

### [SMS Pumping Fraud](/docs/glossary/what-is-sms-pumping-fraud)

SMS pumping fraud happens when fraudsters take advantage of a phone number input field to receive a one-time passcode, an app download link, or anything else via SMS. The messages are sent to a range of numbers controlled by a specific mobile network operator (MNO) and the fraudsters get a share of the generated revenue. 

### [SMS Tracker](/docs/glossary/what-sms-tracker)

An SMS tracker is software that uncovers detailed information about the delivery and content of text and picture messages. It allows anyone to analyze an individual message or group of messages to see delivery patterns, encoding details, and error conditions.
 

### [Sticky Sender](/docs/glossary/what-is-a-sticky-sender)

Sticky Sender is a valuable feature for SMS or Voice marketing where all outbound customer contact comes from a single number. This 'sticky' or 'unchanging' number increases customer familiarity and trust. With a two-way Voice or SMS system, it also allows customers to contact businesses and organizations through the very same number.

### [String Identifier (SID)](/docs/glossary/what-is-a-sid)

A String Identifier (SID) is a unique key that is used to identify specific resources.

### [Studio Flow Context](/docs/glossary/what-is-studio-flow-context)

Studio Flow Context is the data and information captured in a Liquid Template Language by specifying the data type and desired variable.

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## T

### [TCPA](/docs/glossary/what-is-telephone-consumer-protection-act-tcpa)

The TCPA (Telephone Consumer Protection Act) is a federal statute enacted in 1991 designed to safeguard consumer privacy. This legislation restricts telemarketing communications via voice calls, SMS texts, and fax.

### [Toll Fraud](/docs/glossary/what-is-toll-fraud)

Toll fraud, also known as International Revenue Sharing Fraud (IRSF), happens when an application is exploited to generate a high volume of voice calls to the fraudster's own international premium rate numbers. The victim of the toll fraud bears the entire financial responsibility for each minute of the call.

### [TOTP](/docs/glossary/totp)

TOTP stands for Time-based One-Time Passwords and is a common form of two-factor authentication (2FA). Unique numeric passwords are generated with a standardized algorithm that uses the current time as an input. The time-based passwords are available offline and provide user-friendly, increased account security when used as a second factor.

### [Transport Layer Security (TLS)](/docs/glossary/what-is-transport-layer-security-tls)

TLS, or Transport Layer Security, is a widely used cryptographic protocol that ensures data security during communication over a network. The TLS protocol, like its predecessor SSL (Secure Sockets Layer), is primarily designed to enable reliable, authenticated, and secure communication between two or more computer applications. In modern browsers, connections secured with TLS are usually indicated by a lock icon next to the URL.

### [Twilio Markup Language (TwiML)](/docs/glossary/what-is-twilio-markup-language-twiml)

TwiML, or the Twilio Markup Language, is an XML based language which instructs Twilio on how to handle various events such as incoming and outgoing calls, SMS messages and MMS messages.  When building a Twilio application you will use TwiML when communicating your desired actions to Twilio.

### [Two Factor Authentication (2FA)](/docs/glossary/what-is-two-factor-authentication-2fa)

Two-factor authentication (commonly abbreviated 2FA) adds an extra layer of security to your user's account login by requiring two types of authentication. This is usually something your user knows and something they have.

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## U

### [UCS-2](/docs/glossary/what-is-ucs-2-character-encoding)

UCS-2 is a character encoding standard in which characters are represented by a fixed-length 16 bits (2 bytes).  It is used as a fallback on many GSM networks when a message cannot be encoded using GSM-7 or when a language requires more than 128 characters to be rendered.

### [Unicode](/docs/glossary/what-is-unicode)

Unicode is an international character encoding standard that provides a unique number for every character across languages and scripts, making almost all characters accessible across platforms, programs, and devices.

### [UTF-8](/docs/glossary/what-utf-8)

UTF-8 is a variable-width character encoding standard that uses between one and four eight-bit bytes to represent all valid Unicode code points.

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## V

### [Virtual Phone Number](/docs/glossary/what-virtual-phone-number)

A virtual phone number is a standard telephone number that is not locked down to a specific phone. A virtual number can route a voice call or text message to any phone or workflow. With virtual numbers powered by an API, complex software workflows can be built that are triggered by calls and texts.

### [Virtual SMS](/docs/glossary/what-is-virtual-sms)

Virtual SMS enables you to send and receive SMS text messages over the internet without having to use a physical phone. This is especially useful when you want to use software to communicate with telephone networks that would be impossible on a physical phone, e.g. Uber notifying a customer that their car is outside or to have local phone numbers in different countries.

### [Voice API](/docs/glossary/what-is-voice-api)

A PSTN) and applications connected to the internet. By using a voice API, software developers can program voice calling into their applications without specialized telecommunications knowledge and hardware.

### [Voice Proxy](/docs/glossary/what-is-voice-proxy)

Voice Proxy is the technique used to protect users' private information by providing an intermediary number so that neither sender nor receiver can see the other's true phone number during voice calls or SMS exchanges.

### [Voice Trace](/docs/glossary/what-voice-trace)

Voice trace is a voice quality troubleshooting feature that captures the media stream for calls and stores them for Twilio Support to use in their investigations. 

### [VoIP (Voice Over IP)](/docs/glossary/what-is-voip)

Voice Over Internet Protocol (VoIP) is a category of hardware and software that enables voice calls to be made and received over the internet.

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## W

### [Webhook](/docs/glossary/what-is-a-webhook)

HTTP callbacks. They are triggered by some event in a web application and can facilitate integrating different applications or third-party APIs, like Twilio.

### [WebRTC](/docs/glossary/what-is-webrtc)

Web Real-Time Communication (WebRTC) is a collection of communications protocols and APIs originally developed by Google that enable real-time voice and video communication over peer-to-peer connections.

### [WebSockets](/docs/glossary/what-are-websockets)

A WebSocket is a persistent bi-directional communication channel between a client (e.g. a browser) and a backend service. In contrast with HTTP request/response connections, websockets can transport any number of protocols and provide server-to-client message delivery without polling.

### [Workforce Optimization](/docs/glossary/what-is-workforce-optimization)

Workforce Optimization (WFO) is the process of performing quality checks to ensure that all a company staff's interactions with its customers are performed to the same standard

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