A passkey is a way to sign in without a password: your device stores a cryptographic key that you unlock with your fingerprint, face or a PIN. It is based on the FIDO2 standard, like physical security keys such as YubiKey, and it resists phishing because the key only works on the legitimate site.
Related term in this glossary: MFA (multi-factor authentication)
passkey, FIDO2, YubiKey, security key, passwordless authentication