The vocabulary of SMS,
one page per term.

10DLC (10-digit long code) is the US carrier framework under which application traffic from standard 10-digit numbers must be registered per brand and campaign; unregistered A2P traffic is filtered.

A2P (application-to-person) SMS is any text message sent by software to a person: verification codes, alerts, receipts, reminders and marketing campaigns, as opposed to messages typed by one person to another.

Bulk SMS is the sending of one message, usually personalised, to a large list of phone numbers at once through a gateway, typically from an uploaded file or an API batch call.

CPaaS (Communications Platform as a Service) is a cloud platform selling programmable SMS, voice, email and chat through APIs, usually to enterprises on contracts and volume tiers.

E.164 is the international numbering format for phone numbers: a plus sign, the country code and the national number, up to 15 digits, with no spaces, zeros or punctuation.

A flash SMS (class 0 message) is displayed immediately on the phone's screen without being stored in the inbox; support varies by handset and most gateways do not offer it.

An HLR lookup queries a carrier's Home Location Register to learn whether a mobile number is active, which operator serves it and whether it has been ported, without sending a message.

A long number, or virtual mobile number, is a standard-length phone number used as an SMS sender so that recipients can reply, rented per country from a gateway.

MT (mobile terminated) is a message delivered to a phone; MO (mobile originated) is a message sent from a phone, for example a reply or a STOP.

Mobile number portability lets a subscriber keep their number when changing operator, so the prefix of a number no longer guarantees which network will receive the message.

An MSISDN is a mobile phone number in full international form (country code plus subscriber number), the identifier carriers use to route an SMS to a handset.

An OTP is a short numeric code sent by SMS that is valid once and for a few minutes, used to verify a phone number or approve a login or a transaction.

P2P (person-to-person) SMS is a message exchanged between two individuals from their own phones; carriers price and route it differently from application traffic.

A promotional (marketing) SMS advertises a product, offer or event to people who agreed to receive such messages; it must carry an opt-out and respect local quiet hours.

RCS (Rich Communication Services) is the carrier-backed successor to SMS with images, buttons and read receipts; it needs data, a compatible phone and operator support, so SMS remains the fallback.

A short code is a 4- to 6-digit number leased from carriers in one country for high-volume application messaging, with a registration process and a monthly cost.

SMPP (Short Message Peer-to-Peer) is the binary telecom protocol carriers and aggregators use to exchange SMS at high volume; most application senders use an HTTP API instead.

SMS is the text-messaging standard built into every mobile network, carrying messages of up to 160 GSM-7 characters between phones and applications without an internet connection on the handset.

An SMS aggregator is a wholesale intermediary that holds connections to many mobile operators and resells message delivery to gateways and large senders.

An SMS gateway is the service that accepts messages from applications (through an API or a web panel) and hands them to mobile carriers for delivery, returning statuses on the way back.

The SMSC (Short Message Service Centre) is the carrier system that stores and forwards SMS, retrying delivery until the handset is reachable or the validity period ends.

Toll-free SMS uses an 8XX number as the sender for application messages to the US and Canada; it requires a verification process with the carriers before traffic is delivered reliably.

A transactional SMS is a message the recipient expects because of something they did: a login code, an order confirmation, a delivery update or a security alert. It is not marketing and may bypass quiet hours.

Two-way SMS lets recipients reply to your messages; it requires a numeric sender (a dedicated or shared number) because alphanumeric sender names cannot receive replies.

A character counter shows, as you type, the encoding a message will use, how many characters remain in the current segment and how many segments the message will cost.

A concatenated SMS is a long message split into several parts, each carrying a small header so the handset reassembles them in order into one message; each part is billed as a segment.

An emoji in an SMS forces Unicode encoding, cutting the message capacity from 160 to 70 characters, and some emoji take two Unicode units, so a single symbol can add a whole segment.

GSM extended characters are the few symbols (such as €, [, ], {, }, \, ^, |, ~) that the 7-bit alphabet encodes with an escape, so each one counts as two characters toward the 160 limit.

GSM-7 is the default 7-bit SMS alphabet: 128 basic characters covering Latin letters, digits and common punctuation, allowing 160 characters in one message (153 per part when concatenated).

A segment is the unit an SMS is billed in: one 140-byte message part, holding 160 GSM-7 or 70 Unicode characters when alone, 153 or 67 when part of a longer concatenated message.

UCS-2 is the 16-bit encoding used when a message contains characters outside the GSM-7 alphabet; it allows 70 characters per message (67 per part), so non-Latin text costs about twice as many segments.

The UDH is an optional header at the start of an SMS payload that carries control information, most commonly the concatenation reference and part number of a multi-part message.

An alphanumeric sender ID is a text name of 3 to 11 letters, digits and spaces shown as the sender of an SMS instead of a number; recipients cannot reply to it.

A dedicated number is a phone number rented for your exclusive use as an SMS sender in one country, so that replies reach you and recipients can recognise and save it.

A direct route terminates SMS through an agreed connection with the destination operator or its official aggregator, giving reliable delivery, real receipts and honoured sender IDs at the operator's A2P price.

A grey route delivers application SMS through channels not agreed with the destination operator (SIM farms, exploited interconnects), cheaply and unreliably, with fake receipts and sender replacement as common side effects.

A numeric sender ID is a phone number, dedicated or shared, used as the origin of an SMS; it is the only sender type accepted in the Americas and the only one recipients can reply to.

The sender ID is what the recipient sees as the origin of an SMS: an alphanumeric name (up to 11 characters), a short code or a phone number, subject to the rules of the destination country.

Sender ID registration is the process, required in some countries, of declaring an alphanumeric sender name to the local operators or regulator before it is delivered as typed.

Sender replacement is the substitution, by the route or the operator, of the sender you specified with a number or a shared sender, because the destination does not deliver the original.

A shared sender is a numeric sender used by many accounts on a gateway, assigned automatically for one-way traffic where names are not delivered or not yet registered.

A SIM farm is a bank of consumer SIM cards used to send application traffic as if it were person-to-person messaging; operators detect and block it, and its senders lose numbers and names.

An SMS route is the path a message takes from the gateway to the destination operator, through a given carrier or aggregator connection; routes differ in delivery rate, sender fidelity, receipts and price.

Absent subscriber is the carrier reason for a message that could not be delivered because the phone was switched off or out of coverage at every retry; the number is valid and usually delivers later.

Carrier acknowledgement is the confirmation that a destination operator accepted a message for delivery; on routes without handset receipts it is the final positive status, reported as sent.

A carrier error code is the reason attached by the operator to a failed SMS, such as unknown subscriber, absent subscriber, barred or blocked by filter, mapped by gateways to plain-language failure reasons.

Carrier filtering is the blocking or silent dropping of SMS by an operator's anti-spam systems based on content patterns, sender behaviour or volume, often reported as a specific failure reason or not reported at all.

The delivery rate is the share of sent messages confirmed delivered to handsets; it depends on the route, the list quality and the destination, and it is the least useful number in a report when read alone.

A delivery receipt is the status message returned by the carrier for an SMS, reporting that the message was delivered to the handset, failed, or expired, sometimes with an error code.

An expired message is one the carrier could not deliver before its validity period ended, usually because the phone stayed off or out of coverage; it was attempted and is billed like a sent message.

A rejected message was refused by the gateway before sending (invalid number, unsupported destination, blocked content) and costs nothing; a failed message was accepted by a carrier that then could not deliver it, and is billed.

A handset receipt is a delivery receipt generated when the recipient's phone acknowledges the message, the strongest confirmation SMS can give that a text arrived on the device.

Latency is the time between submitting an SMS and its arrival on the handset, typically a few seconds on a healthy route; it is the metric that matters most for one-time codes.

The message status lifecycle is the forward-only sequence an SMS moves through at a gateway: queued, sent, then delivered, failed or expired, or rejected when refused before sending.

Throttling (or pacing) is the deliberate limiting of a campaign's send rate, in messages per minute or spread over hours, so that replies, calls and clicks arrive at a pace the receiving side can absorb.

Throughput is the number of messages a gateway or route can accept and deliver per second (TPS); it decides how long a large campaign takes to leave and is shaped by carrier limits and pacing.

Unknown subscriber is the carrier reason for a message to a number that no longer exists on any network: the number was disconnected, recycled or never allocated. Remove it from the list.

The validity period is how long a carrier keeps trying to deliver an SMS to an unreachable phone before giving up and marking it expired; a gateway lets you set it per message.

An acceptable use policy is the document in which a gateway states what may not be sent through it (illegal content, phishing, impersonation, unsolicited bulk) and what happens when it is.

DLT (Distributed Ledger Technology) registration is India's mandatory system under which every sender, header (sender ID) and message template must be registered with a telecom operator before commercial SMS is delivered.

A DND registry lets subscribers block promotional SMS at the operator level; in India and Nigeria, among others, marketing to DND numbers is filtered by the operators regardless of the sender's consent records.

Under the GDPR (and the ePrivacy rules alongside it), a phone number is personal data and marketing SMS to people in the EU needs consent or an existing customer relationship, plus an opt-out in every message.

KYC is the identity-verification process, mandatory for regulated financial services, that many messaging providers also impose on senders: ID documents, company registration and a review before an account can send.

A no-KYC SMS gateway opens accounts without identity documents, company papers or verification calls, and relies on content rules, consent requirements and route monitoring instead of identity checks.

Opt-in is the recipient's prior agreement to receive SMS from you, required for marketing messages in most countries and best recorded with the number, the date and the source.

Opt-out is the recipient's way to stop receiving your SMS, usually by replying STOP or tapping a link; it must work instantly and permanently for that list.

Quiet hours are the local hours, typically late evening to early morning and sometimes Sundays, during which marketing SMS must not be delivered in a given country; transactional messages are exempt.

Smishing is phishing by SMS: a message that impersonates a bank, a carrier, a delivery company or a public service to make the recipient tap a link or reveal credentials. Gateways block it and close the accounts behind it.

The TCPA (Telephone Consumer Protection Act) is the US federal law that requires prior express consent for automated marketing texts, with statutory damages per message for violations.

An API key is the secret credential that identifies an account to the SMS API; it is sent as a bearer token, scoped to what it may do, and should be created per system and revoked when exposed.

A batch endpoint accepts many messages in one API request, each with its own recipient and text, and returns an individual result per message so that one invalid row does not fail the whole send.

A bearer token is a credential sent in the HTTP Authorization header as \"Bearer <token>\"; whoever holds it can use it, which is why it must travel only over HTTPS and be stored as a secret.

Cursor pagination returns a list in pages using an opaque token pointing at the last item seen, so that new messages arriving while you page do not shift or duplicate results, unlike page numbers.

Exponential backoff is the retry strategy of waiting longer after each failed attempt (1 s, 2 s, 4 s, 8 s…), used for 429 and 5xx responses so that retries do not amplify an overload.

An HMAC signature is a keyed hash (HMAC-SHA256) of a webhook's timestamp and body, computed with a secret shared with your endpoint, so you can verify that the event came from the gateway and was not altered.

An idempotency key is a client-chosen identifier sent with a request so that retrying it after a timeout or error returns the original result instead of sending the message twice.

OpenAPI is the standard machine-readable description of a REST API (endpoints, parameters, schemas, errors) from which typed client libraries, documentation and API tool collections can be generated.

A rate limit is the maximum number of API requests accepted per second (or minute) per key; above it the API answers 429 with a Retry-After header, and batch endpoints are the way to send volume.

A request ID is a unique identifier the API returns in a header on every response so that a specific call can be found in the provider's logs when you contact support.

An SMS REST API lets software send messages and read their status over HTTPS with JSON, using standard verbs and URLs, without a persistent connection or a telecom protocol.

A test key is an API credential that accepts, validates and prices requests exactly like a live key but never sends a message or bills the balance, so an integration can be built before any money is deposited.

A webhook is an HTTPS request the gateway sends to your endpoint when something happens (a message is delivered or fails, a reply arrives, the balance runs low), so you do not have to poll for status.

An affiliate commission is the share of a referred customer's spending paid to the person who referred them; in SMS gateways it is usually a percentage of top-ups for a fixed period, tracked by a link or a code.

The market rate at credit is the exchange rate applied when a confirmed crypto deposit is converted into the USD balance; from that moment the balance is fixed in dollars and no longer follows the coin's price.

Monero (XMR) is the cryptocurrency designed so that amounts, senders and recipients are hidden on chain; paying with it keeps the payment itself private, which matters to senders who chose a no-KYC gateway for privacy.

A network confirmation is the inclusion of a cryptocurrency transaction in a block (and the blocks after it) that makes it final; a deposit is credited once the network considers it confirmed, seconds to an hour depending on the coin.

The network fee is what a blockchain charges to include a transaction, paid by the sender in the coin itself; it varies from fractions of a cent (Tron, Solana) to several dollars (Bitcoin, Ethereum at busy times) and is not set by the merchant.

A prepaid balance is credit deposited in advance and debited per message as traffic is sent; it replaces invoices, cards on file and credit lines, and it is what a crypto-funded gateway runs on.

A stablecoin is a cryptocurrency pegged to a fiat currency, usually the US dollar; USDT (Tether) is the most used one for paying services because a deposit of 100 USDT is credited as about 100 dollars with no exchange-rate risk.

TRC-20 and ERC-20 are token standards on the Tron and Ethereum networks; the same USDT exists on both, but a TRC-20 transfer typically confirms in about a minute for cents, while ERC-20 costs an Ethereum gas fee and takes a few minutes.