parapet
A building summit formed by a small projecting wall along a roof or setback edge, with a straight or irregular ridgeline.
A parapet is a small projecting wall around the edge of a roof or setback. It is very commonly the highest point on a building, because parapets normally occur around mechanical penthouses as well as main roofs. If a parapet overhangs the facade by a greater distance than it rises above the roof, or if it overhangs the facade and is heavily decorated, then it is generally classified as a cornice.
Normal parapets have a straight ridgeline, but parapets can also be irregular, with crenellations, waves, or other patterns.
The wall can surround a mechanical penthouse as well as the main roof. The overhang and decoration conditions in the definition distinguish it from a cornice.