Two-factor authentication calls for a second round of authentication to an account login process. Entering a username – password is a one-factor authentication. Username – Password authentication and then say mobile number or a secret key authentication can be considered as a two - factor authentication.
The different types of credentials for two-factor authentication can be:
Something you know - A PIN, password or a pattern
Something you have – ID, ATM No., Phone No, or an OTP
Something you are – Your Biometrics.