What are a one-time password and an OTP device?

A one-time password is a password usable once and valid for a short time, either time-based or randomly generated, often the second factor in 2FA; an OTP device is software or hardware that generates one-time passwords from an embedded secret key and an input value such as the current time or an incrementing counter.

A single-factor OTP device needs no further factor (for example a classic SecurID token); a multi-factor OTP device requires a PIN or biometric to activate the algorithm (token with keypad). Synonyms: Einmalcode, OTP, Einmal-Passwort-Generator.

Go deeper:

• One-time password (Wikipedia) — HOTP, TOTP and the delivery channels.
• RFC 6238 TOTP — the time-based algorithm behind authenticator apps.