Ultraviolet is a new initiative backed by several big players in the entertainment industry intended to make sense of the digital mess involved in competing media and devices that don't (and can't) agree on one standard format for all movies.
Right now, if I buy a movie on DVD, I only own that movie on that one DVD. If — or more accurately, when — formats change, or I want to watch that movie on a different device, I either have to know how to rip my DVD for my device (something most Lifehacker readers know how to do) or buy a new copy of the movie for a separate device. The idea behind Ultraviolet is that when I buy a movie, I also get a token that, as Wired puts it, represents my ownership of that movie. As long as enough people get on board with this idea, my token would allow me to watch that movie on any device or service that carries the movie, without having to buy another copy.
Ultraviolet's not available at this point, but it's a promising solution to a really annoying problem, and it's worth keeping an eye on. For a great, detailed overview, check out Wired's explanation of the Ultraviolet movie locker.