Barrel/Cartridge Chamber: Holds the grease (either in a cartridge or bulk-loaded).
Pump Mechanism: Can be hand-lever, pistol-grip, pneumatic, or battery powered.
Flexible or Rigid Hose: Directs grease into tight or hard-to-reach areas.
Nozzle/Coupler: Attaches to grease fittings (zerk fittings).
Pressure Output: High enough to force grease into sealed bearings and joints.