PSS (Probabilistic Signature Scheme)
An RSA signature scheme that adds a random salt to every signature, and the variant TLS 1.3 requires for RSA signatures.
Bellare and Rogaway presented PSS in 1996 as a randomised replacement for PKCS#1 v1.5 signatures. The salt means the same message yields a different signature each time, and verification checks the encoding strictly instead of accepting anything that looks plausible.
TLS 1.3 forbids PKCS#1 v1.5 in handshake signatures and requires PSS for RSA. It is one of the rare protocol revisions that made RSA signatures stricter rather than just renaming something.