matte

Sometimes referred to as a holdout matte. An effect that uses information in one layer of video to affect another layer. Mattes are useful when you want to use one clip to selectively hide or reveal part of another; for example, you could use a round spotlight shape to reveal parts of a video layer. You can use a matte effect to mask out areas of a clip or to create alpha channel information for a clip—for example, to make a transparent border around the clip that can be composited against other layers.