What is the term for the overhead upper surface of a room?

The term for the overhead upper surface of a room is "ceiling." This structure serves various functions, including providing a finished appearance to the interior space, concealing electrical wiring and plumbing, and improving acoustics by reducing noise. Ceilings can also be decorative elements that enhance the aesthetic appeal of a room.

In contrast, walls are vertical structures that enclose the sides of a room, defining its boundaries. The floor is the lower surface of a room on which people walk, while the roof is the external upper covering of a building that protects it from weather elements. Each of these terms has distinct meanings within architectural terminology, making "ceiling" the most accurate choice in this context.