Password expiration is the practice of setting a finite period after which a password must be changed. This is important to reduce the risk of a compromised password being used indefinitely by an unauthorized user. A 'Non-expiring password' is not recommended as it could potentially provide ongoing access if compromised. 'Password recovery' is a process to regain access when a password is forgotten, not a method of expiration. Lastly, 'Password storage' is about how passwords are kept, which is unrelated to how often they should be changed.