What is a Digital Copy and what does UltraViolet mean?
A digital copy is just that, a digital copy of the movie that you purchased on DVD or Blu-ray. Many studios offer complimentary digital copies of their films if you buy the DVD or Blu-ray. These digital copies can be played on most computers, tablets (like iPads) and smart phones. Each studio has a different policy in place to oversee their individual digital copies.
UltraViolet (UVVU or UV for short) is an ecosystem for interoperable electronic content. It's a branded set of specifications and agreements along with a centralized rights clearinghouse that allows retailers to sell movies that play on UltraViolet-compatible players and services.
Put another way, UltraViolet is DVD for the Internet. Just as the DVD logo means that you can buy a DVD from any seller and expect it to play in any player with a DVD logo (DVD players, DVD PCs, DVD entertainment systems in automobiles, and so on), the UltraViolet logo means you can buy UltraViolet movies from any seller, keep track of your "virtual library" of movies, and expect them to play on anything with the UltraViolet logo (players, PCs, mobile phones, cable set-top boxes, and so on).