What are movie projectors?

A movie projector is a device that continuously moves film along a path so that each frame of the film is stopped for a fraction of a second in front of a light source. The light source provides extremely bright illumination that casts the image on the film through a lens onto a screen.
There are four major groups of parts that make up a projector:
Spool assembly (cambers, sprockets, claw, motor, platter)
Lamp assembly (bulb, condenser, fan, mirror)
Lens assembly (lens, aperture gate, shutter)
Audio assembly (optical and digital readers, infrared LED)