Software:Collision hull
From HandWiki
Collision hull (also collision mesh or collision geometry) is a computer gaming term for an abstract representation of the 3D world which the player can see. The collision hull provides the logic behind player movement and special actions in the game. It is usually coterminous with the visible representation, but simplified and considered internally distinct by the game engine. It also determines where the player can be "hit". That is called the Hit Box.
For example, what would appear as a stairway in the visible game world may be represented by a flat polygon in the collision hull.
See also