Revocation
Revocation is the mechanism an issuer uses to invalidate a credential after it was issued, for example when a qualification expires or a registration is withdrawn, so verifiers checking it afterwards see it as no longer valid.
Most issuers publish revocation state as a status list: a single compact bitstring where each credential is assigned one bit, published and signed by the issuer so anyone can look up a credential's status without contacting the issuer for every check or exposing which specific credential was checked. A verifier fetches the status list once, checks the relevant bit, and rejects a presentation if the credential has been marked revoked.