Term: Time-based One Time Password [TOTP]

A TOTP is a a one-time password (OTP) generated using the current time as a source of uniqueness.

Common TOTP generators include Google Authenticator, Authy, and others. Each receive a secret key from the service to which they are attached, which is then used in conjunction with the current time to generate a code which is then displayed. The ability to enter that code “proves” you are in possession of your second factor.