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.
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)