Authentication - definition

Authentication is a process of a system to verify the user using a few parameters such as username, passcode, special character, security question, PIN, biometric(fingerprint, facial recognition, retina pattern, etc.), and a few others. To secure the login in a site, place, or portal from unwanted sources authentication is used.

i.e.: To log into a social site such as Facebook or Instagram, the portal requires a user ID and password to authenticate the unique user, if any of the mentioned doesn’t match with the set parameter then it’ll not allow the user to log in.