Projectors were devices which projected an image onto any surface.
When Ben Jackson was trapped in a projection room, filled with cans of film. Briefly playing a western, he rigged up the projector to blind a Cyberman, then stole its weapon and killed it. (TV: The Tenth Planet)
At least in the early film industry, projectors were used to play films at cinemas. The Electro had an exhibit planned involving old celluloid movies. When the opening event came around, though, the wrong tape seemed to play, featuring a group of performers, and the projector wouldn't switch off. The Ghostmaker and Pearl were freed from the celluloid, and took three-dimensional form. (TV: From Out of the Rain)