@vbabka @vitaut At it's core, a passkey is just a "trust on first use" certificate that you can use to authenticate to a website.
Generally the private key is in a password manager or a security key, the website sends a challenge, and your private key signs that. Website validates the signature, and you're in.
But of course, like any good term, passkeys are overloaded and surrounded by thought leadership which makes it hard to track what they are.