Authentication

Verifying the identity of a user, process, or device, often as a prerequisite to allowing access to resources in an information system.
SOURCE: SP 800-53; SP 800-53A; SP 800-27; FIPS 200; SP 800-30

The process of establishing confidence of authenticity.
SOURCE: FIPS 201

Encompasses identity verification, message origin authentication, and message content authentication.
SOURCE: FIPS 190

A process that establishes the origin of information or determines an entity’s identity.
SOURCE: SP 800-21

The process of verifying the identity or other attributes claimed by or assumed of an entity (user, process, or device), or to verify the source and integrity of data.
SOURCE: CNSSI-4009

The process of establishing confidence in the identity of users or information systems.
SOURCE: SP 800-63