Modified stock car racing, also known as modified racing and modified, is a type of auto racing that involves purpose-built cars simultaneously racing against each other on oval tracks. First established in the United States after World War II, this type of racing was early-on characterized by its participants' modification of passenger cars in pursuit of higher speeds, hence the name.

Oval track racing is a form of motorsport that is contested on an oval-shaped race track. An oval track differs from a road course in that the layout resembles an oval with turns in only one direction, and the direction of traffic is almost universally counter-clockwise. Oval tracks are dedicated motorsport circuits, used predominantly in the United States. They often have banked turns and some, despite the name, are not precisely oval, and the shape of the track can vary.