Holographic projection system
A holographic projection system, sometimes shortened to holo-projection system or simply projection system, was the system that made a holodeck function, consisting of a combination of various technologies, such as hologrids and holo-emitters, to create holograms. 

According to The Doctor, his program could only appear in a room equipped with a holographic projection system. ()

See also 
 Photonic field generator
Holographic technology