We all know at least a little about virtual reality, or VR, whether we realize it or not. Just think of films and TV shows, such as TRON, The Lawnmower Man, The Matrix, or Star Trek: The Next Generation. All depict an immersive digital space that people live or work in, and treat as if it's real. The massively multiplayer online role-playing games (MMORPGs), such as World of Warcraft, come close; current VR environments like Second Life edge even closer to being realistic.

Augmented reality, or AR, is different. Wikipedia defines AR as "a live, direct or indirect, view of a physical, real-world environment whose elements are augmented by computer-generated sensory input such as sound, video, graphics or GPS data." Basically, it's a digital overlay on the real world. (Here's a brief history of augmented reality.)