Answer Description
By force expiring all passwords, every network user will be required to change their password at next login. This is a good method to reset all passwords if you suspect some have been obtained maliciously.
Wikipedia
A password, sometimes called a passcode, is secret data, typically a string of characters, usually used to confirm a user's identity Traditionally, passwords were expected to be memorized, but the large number of password-protected services that a typical individual accesses can make memorization of unique passwords for each service impractical Using the terminology of the NIST Digital Identity Guidelines, the secret is held by a party called the claimant while the party verifying the identity of the claimant is called the verifier When the claimant successfully demonstrates knowledge of the password to the verifier through an established authentication protocol, the verifier is able to infer the claimant's identity
Password - Wikipedia, the free encyclopedia