1) in an animation sequence or video edit; short for keyframe(an image used as a starting, ending or reference point); 2) in lighting for video, film, or photography, short for keylight, the principal (and usually brightest) light illuminating the main subject; 3) to switch between two or more video sources, based on a control signal; 4) the control signal used to switch between two or more video sources; 5) an image whose color or brightness as each point is used to determine the switching between two or more video signals.