Rockets contain several systems which contain individual parts. A rocket has two main systems the structure system, which includes the frame, fins etc., and the propulsion system which includes the fuel, nozzle, etc.
Parts of a Rocket
The Structure System includes the nose cone, frame, and fins. The Propulsion system includes the fuel, oxidizer, pumps, and nozzle, The payload and guidance systems are separate from the two main systems
Parts of a Model Rocket
Model Rockets, instead of being composed of systems, aren't. This is because they are so much smaller and don't require pumps, oxidizers, or a nozzle. If there was a propulsion system, it would be made only of the solid rocket engine.