Passkey is what programs aimed at people without favorite Linux distros call WebAuthn+FIDO2(+CTAP2+the rest of the stack you've probably already heard of).
Passkey is a "brand name" for consumers of common workflows under existing WebAuthn+FIDO2 standards. It needed a consumer-oriented brand name because FIDO2 sounds like someone was bad at naming their dog and WebAuthn looks like a cat walked on someone's keyboard. Passkey isn't that much better as a name, but it is better.