The holographic communicator (holo-communicator or holocom for short) was a communication system which allowed two or more parties to send holographic images to each other, simulating face-to-face interaction.
The technology was first in use by the mid 23rd century. By the 2250s holographic communicators were in use throughout Starfleet, with only a few officers such as Captain Christopher Pike still preferring to communicate via traditional view screens. (DSC episode: "Point of Light")
In 2257 the holographic communication systems caused the USS Enterprise to suffer catastrophic systems failures that crippled the starship for an extended period of time. Upon learning that the holographic communicator had been responsible Pike ordered Number One to have Chief Engineer Louvier remove the system from the Enterprise, stating that they would use view screens going forward. (DSC episode: "An Obol for Charon")
In 2273 in the Phase II continuity, when Rear Admiral James T. Kirk met with Heihachiro Nogura in San Francisco, Admiral Carson and Captain Lebutu joined the meeting as full-body holograms. Lebutu showed them visuals of the IKS Amar being destroyed by V'Ger. (Star Trek: Phase II episode: "In Thy Image")
Starfleet continued to refine the system and by 2373 had begun installing it again on ships. Some of the first ships where the system was installed on the bridges included the USS Defiant and USS Malinche. (DS9 episode: "For the Uniform")
During the Dominion War, increased security measures at the Palais de la Concorde led to the decision by the Palais de la Concorde Press Liaison to eliminate in-person press conferences, and instead use holocom technology to allow journalists to attend remotely. This arrangement proved popular enough to continue even after the war. (ST novel: Articles of the Federation)
Starfleet continued to use holographic communication for larger meetings, such as a briefing held during the Gateways Crisis in 2376 and another following the Borg Invasion of 2381. (ST - Gateways novels: Doors Into Chaos, Demons of Air and Darkness, Cold Wars, TNG novel: Losing the Peace)