VJ
VJing (pronounced: VEE-JAY-ing) is a broad designation for realtime visual performance. Wiki
This post by Markus Kreukniet on Passion for EDM blog also gives a good overview of VJ’ing history and some key artists.
VJ Software
There are many softwares you can use for VJ'ing, which is the art of mixing video live. 'VJing is a broad designation for realtime visual performance.' The most popular with VJ's seem to be Resolume and Module8. I'd recommend downloading the trial for Resolume Avenue VJ Software for free from http://resolume.com/