The term 'Wedge Placed Under a Wheel' can be summarized as a Sprag. A Sprag is a mechanical device used to prevent the backward or reverse rotation of a wheel or other rotating part. It is typically a wedge-shaped piece of metal that is placed between two rotating parts, such as a wheel and an axle, to prevent the wheel from rotating in the opposite direction. The Sprag is an important component in many machines and vehicles, as it helps to ensure that the wheel does not rotate in the wrong direction.