Apple Final Cut Pro 7 - Manual (Page 1224)

In Final Cut Pro, a matte is a customizable, polygonal shape used to make part of a clip
transparent. By outlining part of an image with a matte, you can turn everything outside
or inside the shape transparent. Final Cut Pro allows you to create four- and eight-point
mattes.
A four-point matte outlining
the image of the woman The resulting image, with the
background transparent
What Is Keying and How Can You Use It?
Keying refers to the process of turning an area of consistent color or brightness in a video
clip transparent to isolate a foreground subject. The actual keying process results in the
creation of a matte, which is then automatically applied to composite an image with a
background. In television and in movies, keying is used in a variety of ways to composite
actors in front of graphics and other video clips for a variety of effects.
For example, a weather reporter on television often stands in front of a weather map.
The reporter is actually standing in front of a large blue or green screen, but the color is
made transparent (keyed out), and a map is inserted behind the person, instead.
Generating a matte signal using a color signal is referred to as chroma keying, while
generating a matte signal using a black-and-white signal is called luma keying.
1224 Chapter 72 Keying, Mattes, and Masks