About OpenID

OpenID is an open, decentralised single sign-on standard, allowing users to log onto many services with the same digital identity.
An OpenID is in the form of a URL, and is unique in that the user is authenticated by their ‘OpenID provider’ (that is, the entity hosting their OpenID URL). The OpenID protocol does not rely on a central authority to authenticate a user’s identity. Since neither the OpenID protocol nor web sites requiring identification may mandate a specific type of authentication, non-standard forms of authentication can be used, such as smart cards, biometrics, or ordinary passwords.

From Wikipedia