The command deck was an area aboard a starship. It included the ship's bridge. (ENT: "Babel One"; DIS: "The War Without, The War Within")
When Tellarite ambassador Gral returned to Andorian space in 2154, he recalled that, the last time he had been there, he had been "on the command deck of one of our cruisers, driving those "blue demons" back into their territory." (ENT: "Babel One")
Aboard the USS Discovery in 2257, Ensign Taylor was called to the command deck, while Acting Captain Saru arrived at sickbay to see Ash Tyler there. (DIS: "The War Without, The War Within")