In the case of vehicles, the term chassis means the frame plus the "running gear" like engine, transmission, driveshaft, differential, and suspension. A frame is a structural system that supports other components of a physical construction. A subframe is a structural component of a vehicle, such as an automobile or an aircraft, that uses a discrete, separate structure within a larger body-on-frame or unit body to carry certain components, such as the engine, drivetrain, or suspension. The subframe is bolted and/or welded to the vehicle. When bolted, it is sometimes equipped with rubber bushings or springs to dampen vibration.