Masterframe: The combination of the head, sill and jamb sections of a window.
Masonry openings: The openings in a masonry wall left open for windows or doors unit, the same as a rough opening in a frame wall.
Member: Any structural part of a window, such as a rail, stile, or lintel.
Meeting rail: The part of a sliding glass door, a sliding window or a hung window where two sashes meet and create a weather barrier.
Mullion: A wood or metal member used to structurally join two window or door units.
Multi-Lite Sash – A sash divided into many lites.
Muntin: short or light bar, either vertical or horizontal, used to separate glass in a sash into multiple lights. Also called a grille or windowpane divider.