Captain's dining room

From Memory Alpha, the free Star Trek reference.

The captain's dining room or captain's mess was an area aboard Starfleet vessels specifically designed for personal use by the captain in order to entertain guests and eat meals in private. It was generally equipped with food service by means of a kitchen, galley, or replicators. The mess sometimes includes the services of a steward, who brings the meals and drinks to the captain's table.

The NX class had a captain's dining room just off of the ship's mess hall. It was served by the ship's chef. On the Enterprise NX-01, Captain Jonathan Archer often enjoyed a meal with his two senior officers, T'Pol and Charles Tucker, in the captain's mess. (ENT: "Broken Bow")

On Galaxy-class starships, the captain's mess was on Deck 2. It is equipped with a large buffet-style table. (TNG: "Sins of the Father", "Violations")

The captain's mess was a redress of the observation lounge set. The distinctive windows may suggest a location at the very front of that deck, although they do not perfectly match the windows on the USS Enterprise miniature.

Some Intrepid-class ships had a captain's dining room directly behind the mess hall, cabin 125-A on Deck 2. During the USS Voyager's first months in the Delta Quadrant, Neelix converted the captain's dining room into a kitchen area, much to Captain Kathryn Janeway's initial dismay. (VOY: "Phage")

The USS Bellerophon seen in DS9: "Inter Arma Enim Silent Leges" also had a kitchen in place of the captain's dining room, suggesting the modification may be a standard option aboard the Intrepid class. The real-world reason for this was that the Bellerophon set was merely a re-use of the Voyager set.