Crenellations are Not Snack Cakes

A parapet is a low wall, most commonly erected above a roof line, an extension of the facade. 

A crenel is an cut-out in a parapet (thus crenelations), originally employed in battlements for defense.  Crenelations appear in Islamic fortifications of the Fatimid period (969-1171), during the Norman and Gothic periods; and, throughout recent architectural history.

Crenelations, also sometimes referred to as embrasures, crown all manner of projections, turrets and towers.

Atop the twin towers of a Hollywood Heights Cordoban pleasure palace (image #2).

Crenelations aloft a bow window in the Adams-Normandie neighborhood.