AuthenticationAuthentication protocols may use a nonce to prevent replay attacks. A nouce that can only be used once prevents an old message being resent to authenticate.
Cryptographic SaltCryptographic salt is a type of nouce that is added to a string before it is hashed to make the hash more difficult to reverse.
One-time PasswordsA nouce may be generated and then communicated to a user as a one time password. For example, a customer that calls customer support to reset their password may be given a nouce that enables them to perform the reset.
A random number or phrase that is only used once.