What is Multi-factor Authentication?

Multi-factor authentication (MFA) is a method of confirming a user's identity in which a user is granted access only after successfully presenting 2 or more pieces of evidence (or factors) to an authentication mechanism:

1) something they know (e.g. password),

2) something they have, or

3) something they are

A very common second step is a 6 digit number generated by an app that is common to the user and the authentication system.