Glossary

SMS glossary

Plain definitions of the terms that come up in business texting: message parts, sender names, delivery reports, opt-outs and the UK rules.

A2P SMS: A2P SMS (application to person) is any text sent by a business system to a person, such as a reminder, a one-time code or a marketing message.
Alphanumeric sender ID: An alphanumeric sender ID is a business name of up to 11 letters and digits that appears in place of a phone number as the sender of a text.
API key: An API key is a secret string that identifies your account when your software calls an API, so the service knows who is sending and who to bill.
Bulk SMS: Bulk SMS means sending the same text, often personalised with merge fields, to a large list of people at once, such as customers, members or staff.
Concatenated SMS: A concatenated SMS is a long text sent as several linked parts, each with a small header so the receiving phone can join them back into one message.
Delivery receipt: A delivery receipt (DLR) is a status report from the mobile network saying whether a text reached the recipient's phone.
E.164: E.164 is the international phone number format: a plus sign, the country code and the number with no spaces or leading zero, as in +447700900123.
GSM-7: GSM-7 is the standard 7-bit character set for texts, covering plain letters, digits and common punctuation, so one SMS part can hold 160 characters.
Idempotency key: An idempotency key is a unique value sent with an API request so that, if the request is retried, the service recognises it and doesn't act twice.
Long number: A long number is an ordinary full-length phone number used to send and receive business texts; in the UK that usually means a mobile number starting 07.
Marketing SMS: A marketing SMS is any text that promotes a product, service, offer, event or the business itself, which UK law treats as direct marketing.
MEF SenderID Protection Registry: The MEF SenderID Protection Registry is a voluntary UK scheme that helps mobile networks block texts misusing a registered business sender name.
Merge field: A merge field is a placeholder in a text, such as {first_name}, that's replaced with each recipient's own details when the message is sent.
Opt-out: An opt-out is a person's request to stop getting texts from a business, and the business's record of it, so nothing more goes to that number.
P2P SMS: P2P SMS (person to person) means ordinary texts between two people, typed and sent one at a time from a personal phone.
PECR: PECR, the Privacy and Electronic Communications Regulations 2003, is the UK law that governs marketing texts, emails and calls, alongside the UK GDPR.
Sender ID: A sender ID is whatever shows as the sender of a text: either a phone number people can reply to, or a short business name.
Short code: A short code is a short phone number, usually five digits in the UK, that businesses use for text campaigns such as competitions and keyword sign-ups.
SMS aggregator: An SMS aggregator is a company with connections to many mobile networks that carries business texts to phones and passes delivery receipts back.
SMS character limit: The SMS character limit is 160 plain characters for a single text, or 70 if it needs Unicode; longer messages are split into parts and billed per part.
SMS credit: An SMS credit is a prepaid unit used to pay for texts; with CaptiFi Connect, one credit sends one SMS part to a UK mobile.
SMS gateway: An SMS gateway is the software or service that turns a request from a computer system into a text on the mobile network and passes replies back.
SMS part: An SMS part, or segment, is the most text one SMS can carry (160 plain characters, or 70 with Unicode); longer texts go out as several parts.
Soft opt-in: The soft opt-in is the PECR exception that lets a business text marketing to existing customers without consent, as long as strict conditions are met.
STOP keyword: A STOP keyword is a reply word, usually STOP, that a texting platform treats as a request to opt out and acts on without anyone needing to read it.
Test key: A test key is an API key that behaves like a live one but sends nothing and costs nothing, so developers can build and test an integration safely.
Throughput: Throughput is how many texts a platform or route can send in a given time, usually measured in messages per second.
Transactional SMS: A transactional SMS is a text about something a person has already arranged or asked for, such as a booking confirmation, a reminder or a delivery update.
Two-way SMS: Two-way SMS is business texting where customers can reply to the number that texted them, and the replies come back to the business as a conversation.
Unicode SMS: A Unicode SMS uses the UCS-2 encoding so it can carry emoji, curly quotes and non-Latin scripts, but one part then holds only 70 characters.
Webhook: A webhook is an HTTP request one system sends to another the moment something happens, such as a text being delivered or a reply arriving.
Webhook signature: A webhook signature is a code sent with each webhook, usually an HMAC made with a shared secret, that proves the request came from the service.