Whitepaper: Multi-step authentication and why you should use it

Authentication is one of the essential components of security; it is one part of the concept known as Authentication, Authorization, and Accounting (AAA).

Authentication is the process of claiming an identity the proving that you are that claimed identity. Authorization is the mechanism to control what you can access or do. Accounting is the recording of events into a log to review the activities against the rules and policies in order to detect violations or confirm compliance.

SOURCE: net-security.org