The Fenestration Glossary

TERM	MEANING
marine glazing	a u-channel of soft PVC which is wrapped around the edge of the glass, cushioning the glass against the aluminum or vinyl. This process allows for unrestricted expansion and contraction and watertightness
masonry opening	The space in a masonry wall left open for windows or door. The opening in a masonry wall to accept a window or door unit, the same as a rough opening in a frame wall. The header (or lintel) in a masonry opening is usually a steel beam.
meeting rail	the part of a hung window where the two sash meet and create a weather barrier.
mill finish	the original finish produced on aluminum by extruding.
mortise	A slot or rectangular cavity cut into a piece of wood to receive another part.
mortise-and-tenon	A strong wood joint made by fitting together a mortise in one board and a matching projecting member (tenon) in the other.
mullion	an extrusion that joins windows. A wood or metal part used to structurally join two window or door units. The vertical or horizontal divisions or joints between individual windows in a multiple window unit.
mullion	Applies to any short or light bar, either vertical or horizontal, used to separate glass in a sash into multiple lights. Also called a windowpane divider or a grille.
mullion cover	an extrusion that joins panning perimeter legs that extend over existing mullions.
muntin	extrusions in the sash which are exterior (outside of the glass exterior face), internal (in the insulating glass airspace), or true (dividing the glass) which appear to or actually divide the glass into smaller lites
nailing fin	A vinyl or metal flange integrated into (or attached to) the perimeter of a window frame for installation onto the rough opening’s header, jack studs and rough sill. A continuous nailing fin may surround the frame as with an all-vinyl window or a nailing fin may be affixed to the head and side jambs as with a vinyl clad window frame.
neoprene	a synthetic rubber having physical properties closely resembling those of natural rubber. It has extremely good weather and temperature resistance, both heat and cold, with ultraviolet stability.
nite latch	hardware which, when extended, restricts the sash opening to a predetermined dimension.
obscure glass	mainly used for decoration, diffusion, or privacy. The pattern is rolled into the hot glass during glass manufacturing.
operating unit	A window or door that opens -- also referred to as a vent unit or operator.
operator	A metal arm and gear device which allows for easy opening and closing of projecting windows; e.g. casement and awning windows.
oriel window	a window with unequal sash.
orientation	The compass direction that a structure faces. To optimize heat-gain, the major facade of a building should face South (a variation as much as 30 degrees east or west of south will not seriously affect performance).