A generic term for any secret value that is used to verify the subscriber in an authentication protocol. These are further divided into short-term authentication secrets, which are only useful to an attacker for a limited period of time, and long-term authentication secrets, which allow an attacker to impersonate the subscriber until they are manually reset. The authenticator secret is the canonical example of a long-term authentication secret, while the authenticator output — if it is different from the authenticator secret — is usually a short-term authentication secret.
Sources:
NIST SP 800-63-4
[