Based on FIDO Alliance and W3C standards, passkeys replace passwords with cryptographic key pairs. These key pairs profoundly improve security. – https://developer.apple.com/passkeys/

Based on FIDO2/WebAuthn but unlike them, passkeys are those things Apple & Google have been pushing that live on their servers + one specific device in its secure enclave you as as a user aren’t allowed to look into. FIDO2 is usually tied to some USB security token.