A communications system that projects a life-size holographic image of the other party into the room, trialled aboard the USS Defiant in 2373 and shown as common in the 2250s in Discovery.
A holographic communicator replaces the viewscreen with a three-dimensional image of the person calling, who seems to stand in the room with the speaker.
In Deep Space Nine it is presented as new. A unit is installed on the Defiant's bridge in For the Uniform, where Benjamin Sisko uses it to talk to Captain Sanders and to trade threats with the Maquis leader Michael Eddington. It is seen again in Doctor Bashir, I Presume and then quietly dropped.
Discovery, set a century earlier, shows Starfleet officers routinely holding holographic conversations. The episode An Obol for Charon offers an explanation for their absence from Kirk's ship: Christopher Pike, blaming the system for a string of failures aboard the Enterprise, orders it removed for good.