In a Probabilistic Signature Scheme, the signature depends on a random input, in addition to the private key and message.
Probabilistic signature scheme opposes to deterministic signature scheme.
RSASSA-PSS, ECDSA, and ISO/IEC 9796-2 scheme 2 are common probabilistic signature schemes.
RSASSA-PKCS1-v1_5, EdDSA, and ISO/IEC 9796-2 schemes 1 and 3 are common deterministic signature schemes.