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SMS verification glossary

Twenty terms you meet when dealing with verification codes and temporary numbers, defined in one sentence each, with a longer page behind every one.

What is SMS verification?

SMS verification is the process where a service sends a one-time code by text message to a phone number and asks you to type it back, proving you control that number. It is used at sign-up and as a second factor at login.

OTP (one-time password)
An OTP is a code valid for a single login or action, usually 4 to 8 digits, sent by SMS, email or generated by an app, that expires after a few minutes.
Two-factor authentication
2FA requires two independent proofs to log in: something you know (password) plus something you have (a phone receiving a code, an authenticator app or a hardware key).
VoIP number
A VoIP number is a phone number delivered over the internet rather than a mobile carrier SIM; apps can detect this through a carrier lookup and often refuse it for verification.
Non-VoIP number
A non-VoIP number is a line from a mobile carrier (a physical SIM), which passes the line-type checks that reject internet-based numbers.
Virtual number
A virtual number is a phone number not tied to a SIM in your own phone: it is hosted by a provider and forwards its SMS to a web dashboard or an API.
Temporary number
A temporary number is a real phone number reserved to you for a short time, typically 20 minutes, to receive one verification SMS, after which it returns to the pool.
Activation
In number marketplaces, an activation is one purchase of a temporary number for one service: the number is reserved, receives the code, and the order is closed.
Number rental
A number rental keeps the same phone number for a fixed period (24 hours to 30 days) with unlimited incoming SMS, for accounts that need repeated verification.
SIM swap
A SIM swap is an attack where someone convinces a carrier to move your number to their SIM, then receives your verification codes and resets your accounts.
Short code
A short code is a 5- or 6-digit sender number used by businesses to send high-volume SMS such as verification codes; many virtual numbers cannot receive from short codes.
10DLC
10DLC (10-digit long code) is the US system for businesses to send application SMS from regular 10-digit numbers, with registration and throughput rules set by carriers.
E.164 format
E.164 is the international phone number format: a plus sign, the country code and the national number with no spaces, up to 15 digits, e.g. +14155552671.
Country calling code
A country calling code is the one- to three-digit prefix (after the plus sign) that routes a call or SMS to a country: +1 for the US and Canada, +44 for the UK, +55 for Brazil.
eSIM
An eSIM is a SIM profile downloaded to a device instead of a physical card; for verification purposes it behaves like a carrier line, not like VoIP.
Smishing
Smishing is phishing by SMS: a text pretending to come from a bank or service, with a link or a request for a code, to steal credentials.
Carrier lookup
A carrier lookup is a query that returns the carrier and line type (mobile, landline, VoIP) of a phone number; apps run it before sending an OTP.
Success rate
Success rate, in a number marketplace, is the share of recent activations for an app and country that received the SMS; it is the best predictor of whether your next number will work.
Second-line apps
Apps that give you a second line on your own phone for calls and texts, billed monthly; the numbers are VoIP and most verification flows reject them.
API key
An API key is the secret string that identifies your account in API calls; it is created in the dashboard and can be rotated at any time.
SMS-Activate protocol
The SMS-Activate protocol is the de facto API standard of number marketplaces (getNumber, getStatus, setStatus, getBalance, getPrices), implemented by many providers so registration tools work across them.

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