Authentication

The process to verify that someone is who they claim to be when they try to access a computer or online service.

The process of verifying the identity or other attributes of an entity (user, process, or device).

Extended Definition: Also the process of verifying the source and integrity of data.

Adapted from: CNSSI 4009, NIST SP 800-21, NISTIR 7298

https://en.wikipedia.org/wiki/Authentication