In military language, a missile, also known as a guided missile, is a guided self-propelled flying weapon usually propelled by a jet engine or rocket motor. This is in contrast to an unguided self-propelled flying munition, referred to as a rocket (although these too can also be guided). Missiles have four system components: targeting or missile guidance, flight system, engine, and warhead. Missiles come in types adapted for different purposes: surface-to-surface and air-to-surface missiles (ballistic, cruise, anti-ship, anti-tank, etc.), surface-to-air missiles (and anti-ballistic), air-to-air missiles, and anti-satellite weapons. Non-self-propelled airborne explosive devices are generally referred to as shells and usually have a shorter range than missiles. In ordinary language the word means an object which can be thrown, shot, or propelled toward a target.