OpenID

OpenID is an open standard that describes how users can be authenticated in a decentralized manner, eliminating the need for services to provide their own ad hoc systems and allowing users to consolidate their digital identities. Users may create accounts with their preferred OpenID identity providers, and then use those accounts as the basis for signing on to any website which accepts OpenID authentication. The OpenID standard provides a framework for the communication that must take place between the identity provider and the OpenID acceptor (the 'relying party').

‒ Courtesy of Wikipedia