Definitions of Terms under Alphabet M

In glazed lite assemblies, thin vertical and horizontal divider bars, which give the lite a multi-paned look. Muntins may be part of lite frames, and on the outside surface of the glass, or assembled between glass in insulated glass units.

Multiple Extension Unit

In patio door assemblies, a fixed door panel in a separate frame, edge-joined to a patio door unit to add another glass panel to the installation.


A post or divider which runs from sill to frame top in multi-panel doors, or sidelite assemblies.


A short term for mullion. Used to describe the edge-joining of two door units or sidelites together.

Mortise-Type Lock

A lock-set, which is housed into a deep recess cut into the edge of a door.


A recess cut into the surface or edge of a part, usually for the purpose of housing hardware such as hinges, latch plates etc.


An angled cut across the end of a lineal part, usually done to join with a similarly cut part at a corner. Most typically used in casing.