OpenID is an open standard that allows users to be authenticated by co-operating sites
OpenID is an open standard that allows users to identify themselves to websites by means of a URL which either points directly to an OpenID authenticator, or points to to a page which contains redirection details to such an authenticator. The original website can know with confidence that the user has authenticated themselves to the delegated site, but doesn't know any of the tokens that were used by the user to perform this authentication.
OpenID differs from google or facebook in that the user controls which authentication engine is used, and no information other than the success or failure of the authentication is passed to the calling website.
OpenID allows you to use an OpenID account to sign in to multiple websites, without needing to create new passwords / identities.
Website: http://openid.net
Wikipedia: http://en.wikipedia.org/wiki/Openid
