What does "Multi-Factor Authentication" mean?

Multi-Factor Authentication:

Multi-Factor Authentication ["MFA"] is an automated system that authenticates someone's right to view or change information about them in an account on a website; such things as a answering security questions correctly, inputting a code sent via text or telephone or email, and so on, are the "factors" that are used to authenticate a valid user and defeat an unauthorized third party from getting into the account. Compares with Two Factor Authentication.

 Wiki: Multi-Factor Authentication