The wheels which actually drive the vehicle along. In the case of a steam engine these will be the large wheels in the middle of the locomotive connected together by coupling rods. They may sometimes have smaller wheels either in front of behind them - see wheel arrangements for more details.
Wheel that transmits motion and force, by receiving power from the engine by means of the connecting rod.
It is the wheel that not only supports the vehicle but also moves it because it is connected to the propulsion engine elements. A drive wheel can also be the leading wheel.