A collision area is a restricted area on the screen that cannot be overwritten by pointer drawing. See MOU_MARKCOLLISIONAREA.

Function 57h frees the current collision area for a session so that the pointer can be drawn anywhere on the screen. If a collision area was declared for the session, the collision area is freed and the pointer position is checked. If the pointer was in the freed area, it is drawn. If the pointer was not in the freed area, no pointer manipulations take place.