The word "楼上" is formed through the direct, spatial combination of its two constituent characters: "楼" (lóu), which means "building" or specifically "a floor/level of a building", and "上" (shàng), which means "above" or "up". Placing "上" after "楼" creates a simple locative phrase meaning "the floor above" or, by common usage, "upstairs", where the second character specifies a positional relationship to the first.