- a reaction engine that produces a thrust due to an exhaust consisting entirely of material, as oxidizer, fuel, and inert matter, that has been carried with the engine in the vehicle it propels, none of the propellant being derived from the medium through which the vehicle moves.
- a reaction engine in which a fuel and oxidizer are burnt in a combustion chamber, the products of combustion expanding through a nozzle and producing thrustAlso called: rocket motor
- An engine used to produce a jet of hot gases to propel a rocket. The jet is produced by combustion of a fuel with other chemicals stored in the rocket. Since they do not rely on the oxygen in the atmosphere for combustion, rocket engines can operate in space. Compare turbojet.