‘Blue Screen’ is a common name for a special effects technique. By filming a subject in front of a large blue screen, the editor can later replace the blue screen with any kind of background, to make it appear as if the subject is for example in space, the desert, or on a deserted island. To see how Biz Kid$ uses a blue screen click below:
http://www.youtube.com/watch?v=9osNaXSFxfs&feature=channel_page