In architecture, a cupola consists of a dome-shaped ornamental structure located on top of a larger roof or dome, often used as a lookout or to admit light and provide ventilation. The word comes, through Italian, from the lower latin 'cupula' (classical latin 'cupella' from the greek 'kupellon') small cup (lat. 'cupa') indicating a vault resembling an upside down cup.
In some cases, the entire main roof of a tower or spire can form a single cupola. More frequently, however, the cupola comprises a smaller structure which sits on top of the main roof. If the cupola can be reached by climbing a stairway inside the building, it is referred to as a belvedere or widow's walk. Some cupolas, called lanterns, have small windows which illuminate the areas below.