Passkeys are sets of two cryptographic keys: a public key that's registered with the online service or app, and a private key that's stored on a device, such as a smartphone or a computer.
That might sound complicated, but passkeys have been designed to be easy to use. In fact, to log in with a passkey, you use your face, a fingerprint, or a PIN in much the same way that you unlock your smartphone.
The advantage of passkeys is that even if a hacker gets their hands on a website's public key, your account is still locked because they don't have access to the private key on your device.