An area within a building enclosed by walls and floor and ceiling WordNet 3.0 & Open English WordNet

In a building or large vehicle, like a ship, a room is any space enclosed within a number of walls to which entry is possible only by a door or other dividing structure that connects it either to a passageway, to another room, or to the outdoors, that is large enough for several people to move about, and whose size, fixtures, furnishings, and sometimes placement within the building or ship support the activity to be conducted in it. Wikipedia

Enclosed space in a building. Wikipedia Disambiguation

A separate part of a building, enclosed by walls, a floor and a ceiling. Wiktionary