TOTP
Also called: Authenticator app code
Time-based one-time password: an authenticator app and the server compute the same code every 30 seconds.
Definition
Both sides use a shared secret and the current time, so a phone with a wrong clock produces codes the server rejects. Servers usually accept one step either side to allow small differences.
In practice
Google Authenticator shows a new 6-digit code every 30 seconds for your bank account.
Learn it in context
Lessons that use this term.