The password itself is not stored in AD in decryptable form. As I understand it what is stored is a hash of the password and the date/time when the password was set. When a user logging on enters the password that value and the date/time when the password was last set are used to re-calculate the stored hash. if this is the same as the stored hash, the assumption is that the user entered a valid password.
Full Definition of CREDENTIAL. 1. : something that gives a title to credit or confidence; also: qualification 3a. 2. plural: testimonials or certified documents showing that a person is entitled to credit or has a right to exercise official power.
For other uses of the terms authentic and authenticity, see Authenticity. Authentication (from Greek: Î±á½Î¸ÎµÎ½ÏÎ¹ÎºÏÏ authentikos, real, genuine, from Î±á½Î¸Î­Î½ÏÎ·Ï authentes, author) is the act of confirming the truth of an attribute of a single piece of data (a datum) claimed true by an entity.