Key: 1) A signal that can be used to electronically "cut a hole" in a video picture to allow for insertion of other elements such as text or another video image. 2) The composite effect created by cutting a hole in one image and inserting another image into the hole.

Keyer: A device used to extract the foreground elements from a background allowing the insertion of a new background.

Key Frame: A video frame in which all of the video information is recorded in compressed fashion. If the clip has a large amount of motion, better playback will occur with every frame being a Key Frame. If there is very little motion, such as a narrator, a higher number of Delta Frames will give satisfactory playback.

Keying: The process of replacing part of one video image with video from another image. As opposed to mixing images together, keying "cuts" one image cleanly into another.

Key Light: The term used to describe a subject's main source of illumination. When shooting outdoors, the key light is the sun.