A matte object is invisible but blocks any geometry behind it. However, it does not block the background.

Matte object reveals part of the background, making the hamburger geometry appear to be inside the oven.

For example, you might make a complex scene for the background of your animation, render it once, then assign the resulting bitmap as a background using only a few animated objects during the rendering of the animation. If you then needed one of your objects to appear from behind some portion of the background, such as a building, you would create a matte object that matches the building. You then place the animated object behind it. The bitmap image of the building appears, but the animated object is blocked until it moves from behind the matte object.

Matte objects, though invisible, can cast shadows.

Matte objects can also receive shadows. When the Matte/Shadow material's Affect Alpha check box is set, shadows cast on the matte object are applied to the alpha channel. This lets you render maps with alpha shadows that you can composite later. To properly generate shadows on a matte object, turn off the Opaque Alpha check box and then set the Affect Alpha check box.