In a motor vehicle, the term drivetrain, powertrain or powerplant refers to the group of components that generate power and deliver it to the road surface, water, or air. This includes the engine, transmission, driveshafts, differentials, and the final drive (drive wheels, continuous track like with tanks or Caterpillar tractors, propeller, etc.). Sometimes "powertrain" is used to refer to simply the engine and transmission, including the other components only if they are integral to the transmission. In a carriage or wagon, running gear designates the wheels and axles in distinction from the body.
A motor vehicle's driveline consists of the parts of the drivetrain excluding the engine and transmission. It is the portion of a vehicle, after the transmission, that changes depending on whether a vehicle is front-wheel drive, rear-wheel drive, or four-wheel drive.
In a wider sense, the power-train includes all of its components to transform chemical, physical or nuclear energy into secondary energy and deliver it to the interface to the outer world for propulsion purposes. This includes the utilization of multiple power sources and non–wheel-based vehicles.