A machicolation is an opening in a medieval castle for dropping rocks or boiling water on an enemy. It’s like a sneaky window in a castle that lets people drop stuff on their enemies to keep them from coming in.
A machicolation is an opening — or series of openings — in a projecting parapet (low wall, like a ledge) between corbels (triangular brackets) on a medieval castle. You might forget those architectural terms, but you should remember what a machicolation is for: dropping stuff on invaders. The machicolation allows people in the castle to drop stones, boiling water, or other weapons on people attacking the castle. This is a great way to defend the castle without going outside.