Definition:
A glacis is an artificial slope outside of a fortress which forces attacking troops to remain under fire until reaching a ditch or moat near the walls. The glacis allows the defenders to have a direct line of fire with minimal changes in angle. Also, the glacis serves an additional defensive purpose by preventing direct artillery fire against a fortress' walls.
In modern usage, the term glacis is used to refer to the sloped, front section of a tank or armored vehicle's hull.
