Access control is the method by which systems determine whether and how to admit a user into a trusted area of the organization — achieved by a combination of policies, programs, and technologies. Three related terms:

• Identification — claiming an identity.
• Authentication — Who goes there? Determining whether access is allowed (proving the identity is real).
• Authorization — Are you allowed to do that? Enforcing limits on the actions of an authenticated user.

Note: "access control" is often used as a synonym for authorization.