What is multi-factor authentication and what are its factors?

Multi-factor authentication, or MFA, requires users to present at least two different types of evidence to verify their identity. The three factor categories are something you know like a password or PIN, something you have like a smart card, hardware token, or phone with authenticator app, and something you are like a fingerprint, face scan, or iris pattern. True MFA uses factors from different categories. Two passwords are not MFA because both are something you know. A password plus a push notification to a registered phone is MFA.