Visual communication, also known as two-way visual contact or comm-pic was a means used in establishing subspace communications between two parties on a viewscreen.
According to Commander Spock in 2266, during the Earth-Romulan War there was no ship-to-ship visual communication, therefore, no Human, Romulan, or ally had ever seen the other. (TOS: "Balance of Terror")
Space station Regula I communicated with the USS Reliant and USS Enterprise via comm-pic in 2285. (Star Trek II: The Wrath of Khan)