Holographic projector

A holographic projector (also called a holographic emitter or holo-emitter for short) was a device used to project holograms.

By the 2360s, holographic projectors were installed aboard Starfleet starships in specialized areas called holodecks. 

By the 2370s, ships such as the USS Voyager had holo-emitters installed in their sickbays to enable the use of the Emergency Medical Hologram.