MDF:Medium-density fiberboard. A wood-fiber composite used in a variety of window, door and millwork applications.
Mortise lock:A lock fitting a rectangular-shaped cavity in the edge of a door.
Mullion:A component used to structurally join two window or door units.
Multipoint lock:A locking system, operated with one handle that secures a window or door at two or more locking points.
