https://webauthn.guide/ https://webauthn.guide/ has a lot of detail if you want to go into it, but what they're referencing here is the "rp" or "relying party"

https://webauthn.guide/ https://webauthn.guide/ has a lot of detail if you want to go into it, but what they're referencing here is the "rp" or "relying party" field that's used as part of the credential setup. This uses browser APIs to share the origin of the credentials stored with your hardware token to guarantee that your private key is only used when visiting that same service. This is as opposed to TOTP as a second factor where you're relying on the user to verify that they're not putting it into a phishing website.