1A room in a hotel, restaurant, bar, etc., in which food or drink is served to customers or diners.
2A room in a large house or institution in which food from the kitchen is made ready to be served in the dining room.
serving room/ˈsəːvɪŋ ruːm/ /ˈsəːvɪŋ rʊm/
Early 19th century (in an earlier sense). From serving + room.