What is a space module?

The Apollo spacecraft had 3 modules:

The Service Module (SM): This was the main workhorse of the Apollo spacecraft once it was Low Earth Orbit. It contained a powerful engine that was used to make course corrections, slow the craft down to enter lunar orbit, and finally to propel the craft back away from the moon for the return trip. It also contained the main communication equipment, the life support system (also known as Environmental Control System, ECS for short), the main electrical system, and, on A-15, A-16, and A1-17, the Science Instrument Module.

The Command Module (CM): The CM, sometimes referred to as the capsule, is the cone-shaped spacecraft that connects to the SM (creating what was called the CSM, or Command/Service Module). The CM is where the astronauts "lived" while in transit between the Earth and the moon, and then back home again. It contained all the controls, three seats (called couches) where the astronauts sat during take off and splashdown, as well as the docking mechanism and tunnel for joining to and entering the Lunar Module (see below). Once the mission was over and the spacecraft was had completed its journey back to Earth, the CM jettisoned the SM, exposing the blunt heat shield used to protect the fragile human occupants on-board during the intense heat of reentry.

The Lunar Module (LM): The LM was the spacecraft used to ferry two astronauts out of lunar orbit and down to the surface, as well as provide them with shelter during their stay. The LM was actually two separate spacecraft in one: The Descent stage, which had a large engine and ample storage room in order to carry all the scientific and life support equipment down to the surface, including the Lunar Rover (LRV) and the ALSEP (Apollo Lunar Surface Experiment Package), and the Ascent stage, which, similar to the CM above, was the astronaut's living quarters during surface operations and their cockpit during flight. Once the surface mission was complete, the Descent stage was disconnected from the Ascent stage, which had its own less powerful engine, and the Descent Stage became a stable platform from which the astronauts could ensure they had a perfectly aligned launch back into orbit.