One time passwords (OTPs) are an authentication method used as part of two-factor authentication (2FA) and multi-factor authentication (MFA):
Something you know (Username/Password)
Something you have (One Time Password)
OTPs are unique passwords that are only valid for a single login session for a defined period of time. OTPs are generated via the open standard OATH HOTP (event-based) or TOTP (time-based) algorithm. A variety of user authenticators can be used to generate OTPs, or they can be generated separately and sent to users via SMS, IVR, email or other means.