SMS glossary: gateway, API and messaging terms explained
Short definitions of the terms that come up when you send SMS from software: gateways and APIs, sender IDs and number types, encodings and segments, consent rules and delivery reports. Each entry gives the one sentence answer first, then how the term works, then what it means when the gateway is an Android phone with a SIM. Terms link to the tools, docs and country pages where they matter.
Updated
- 10DLC10DLC (ten-digit long code) is the United States system for sending application-to-person SMS from ordinary ten-digit phone numbers, with the sending brand and its campaign registered and verified in advance.Updated September 5, 2026
- A2P and P2P messagingP2P is a text one person sends to another; A2P is a text an application sends to a person, and carriers apply different rules, filters and prices to each.Updated September 5, 2026
- Alphanumeric sender IDAn alphanumeric sender ID replaces the sending phone number with a short text string such as a brand name, up to eleven characters, on routes and in countries that support it.Updated September 5, 2026
- Concatenated SMSA concatenated SMS is a message longer than one segment that the sender splits into several SMS carrying a shared header, so the receiving phone can reassemble them into one text.Updated September 5, 2026
- Delivery receiptA delivery receipt is the network's report that an SMS reached the recipient's handset, or failed to, surfaced by a gateway as a status on the message.Updated September 5, 2026
- DLT registrationDLT registration is the Indian requirement that any business sending commercial or transactional SMS register itself, its sender headers and its message templates on a distributed ledger run by the telecom operators, under TRAI rules.Updated September 5, 2026
- DND registryA DND (Do Not Disturb) registry is a national list of phone numbers whose owners have opted out of promotional calls and texts, which senders and operators must check before sending marketing.Updated September 5, 2026
- E.164E.164 is the ITU standard for international phone numbers: a plus sign, the country code, and the national number with no spaces or punctuation, at most fifteen digits.Updated September 5, 2026
- GSM-7GSM-7 is the default 7-bit character set for SMS, defined in 3GPP TS 23.038, which fits 160 characters into the 140 bytes of a single text message.Updated September 5, 2026
- Long codeA long code is a standard full-length phone number, such as a ten-digit United States number, used as the sender of SMS.Updated September 5, 2026
- MMSMMS (Multimedia Messaging Service) is the carrier messaging service for pictures, audio, video and long text, delivered over the mobile data connection rather than the signalling channel SMS uses.Updated September 5, 2026
- Opt-inOpt-in is the recipient's recorded agreement to receive text messages from you, collected before the first message and kept as proof, with a higher written standard for marketing.Updated September 5, 2026
- OTPAn OTP (one time password) is a short code valid for a single login or action and a short time, most often delivered by SMS to prove the user holds the phone number on the account.Updated September 5, 2026
- RCSRCS (Rich Communication Services) is the carrier messaging standard meant to succeed SMS, adding read receipts, typing indicators, high-resolution media, group chat and verified business senders, delivered over data.Updated September 5, 2026
- Sender IDThe sender ID is what the recipient sees in the from field of a text message: a phone number, a short code, or a registered brand name.Updated September 5, 2026
- Short codeA short code is a five or six digit phone number leased for high-volume application-to-person SMS within a single country.Updated September 5, 2026
- SIM boxA SIM box is a device holding many SIM cards that routes bulk calls or messages through consumer subscriptions to avoid wholesale charges, and carriers actively detect and block it.Updated September 5, 2026
- SMPPSMPP (Short Message Peer-to-Peer) is the binary, persistent-connection protocol that message centres, aggregators and high-volume senders use to exchange SMS with mobile networks.Updated September 5, 2026
- SMS APIAn SMS API is a programmatic interface, almost always HTTP, that lets software send text messages, read the ones that arrive, and check what happened to each one.Updated September 5, 2026
- SMS gatewayAn SMS gateway is the piece of software or hardware that takes a message from an application and hands it to a mobile network so it arrives as a text on a phone.Updated September 5, 2026
- SMS gateway appAn SMS gateway app is an Android application that turns a phone with a SIM into an SMS gateway: it receives send requests from an API over the internet and sends them as texts through the phone's SIM, and forwards texts the phone receives back to your software.Updated September 5, 2026
- SMS segmentAn SMS segment is one physical text message of up to 140 bytes, the unit that networks carry and providers bill, so a long or non-Latin message counts as several segments.Updated September 5, 2026
- SMS throughputSMS throughput is the number of messages a sender can push into the network per unit of time, and it is set by the sender type: a handset, a long code, a short code or an SMPP bind each have their own ceiling.Updated September 5, 2026
- STOP keywordSTOP is the conventional reply a recipient sends to opt out of a sender's text messages, which the sender must recognise and honour by ending the messages and confirming once.Updated September 5, 2026
- TCPAThe TCPA (Telephone Consumer Protection Act) is the United States law, implemented by the FCC in 47 CFR 64.1200, that requires prior express consent before automated calls or texts and written consent before marketing ones.Updated September 5, 2026
- TOTPTOTP (time-based one time password) is a code an authenticator app computes from a shared secret and the current time, so it works offline and needs no message to be sent.Updated September 5, 2026
- Two-way SMSTwo-way SMS is messaging where recipients can reply to the number that texted them and the sender's software receives and acts on those replies.Updated September 5, 2026
- UCS-2UCS-2 is the 16-bit character encoding SMS falls back to when a message contains any character outside the GSM-7 alphabet, which limits one segment to 70 characters.Updated September 5, 2026
- Virtual numberA virtual number is a phone number not tied to a SIM or a physical line, allocated from a provider's inventory and routed over the internet to whatever application or device the owner configures.Updated September 5, 2026
- WebhookA webhook is an HTTP request a service sends to a URL you own when something happens, so your code learns about an inbound SMS or a delivery event the moment it occurs instead of polling for it.Updated September 5, 2026