Motion Capture is a method of animating 3D characters by using the movements of real people. This saves on the time needed to key-frame all the motions of the limbs of the body, which is a time consuming process. Motion Capture, or mocap, is used all over the motion picture industry now and world famous movies such Avatar, Happy Feet and Lord of the Rings have used mocap to produce realistic character animation. The method produces movements which are very life-like but which in turn has resulted in some controversy as to whether animations of this kind are indeed animations! (Read more about this here)