Short bio: Computer Scientist, FOSS supporter (read more)
Tux Machines (TM)-specific
OpenID is an open decentralized digital identity system that has been gaining traction in recent months. It implements a solution to some everyday headaches such as single-sign-on, but it does not address related issues like privacy, trust, spam prevention, or message authentication. OpenID uses a multiple-stage sign-on process, but don't let that discourage you. As an end user, the benefits are stacked in your favor.
As the most basic level, your OpenID identity is a unique URL. It can be a URL that you directly control (such as that of your personal Web page or blog) or one provided to you by a third-party service, such as an OpenID provider. In that sense, a site's use of OpenID identities is no different than using email addresses as identifiers: they are unique to each user and are verifiable. But you can publicly display an OpenID identity without attracting spam.
Using your OpenID to sign in to a compliant site involves four parties: you, whatever site hosts your OpenID URL, the site to which you are signing in, and an "identity server" which brokers the authentication between you and the site to which you are signing in. In the official OpenID parlance, the site to which you are signing in is referred to as the "consumer."