A spoiler is a kind of wing that is mounted on the rear of the car in a horizontal position. Its function is to provide high speed stability. For most cars, the spoiler is purely cosmetic; a car has to be going over 100 mph to take advantage of the aerodynamics of the spoiler. Some mini-vans also make use of a spoiler, but it's upside down, and angled. The purpose of this type of spoiler is simply to keep the rain off the rear window.