Greenscreen (sometimes also referred to as bluescreen), refers to the solid background color used when filming a shot. Generally, the greenscreen is placed in the shot where it will later be remove as a post process. Once removed, the resulting transparency will be replaced by footage from another shot, or a completely computer generated environment. To “pull” a matte, means to extract a grayscale matte that you can use in compositing of two or more shots together. This is the key step in handling greenscreen footage.