Awning: A single (or double) operating window in which the bottom of the sash swings outwards for ventilation

Astragal: The exterior center post or moulding on a double door (attached to the secondary or inactive door panel)

Bay: Three connected windows (usually made up of a larger fixed window in the center and two smaller operating windows on either side) in a 30 degree or 45 degree angle formation

Bow: Four or more connected windows (fixed or operating) in a 10 degree or 15 degree angle formation

Brickmould: An exterior moulding around the window (to seal and cover the exposed window opening, insulation, interior jambs etc…)

Casing: The interior decorative moulding/trim that covers the inside edge of the jambs and the rough openings between the window and the wall

Double glazing: The use of two panes of glass (in a window frame) to increase energy efficiency and to provide other performance benefits

Double hung: A window with two vertical operating sashes that slide up-and-down for ventilation

Drip cap: An exterior aluminum moulding placed on the top of the brickmould or capping of a window frame

Egress window: A window large enough for exit in case of an emergency

Fixed: Non-opening or non-operating window

Flashing: Aluminum attached to the outside of the head or side jambs of a window to provide a weather barrier (preventing leakage between the frame and the wall)

Gasket: A weatherstrip used to create a watertight seal between the sash and the window frame

Glazing: The glass panes in the sash of a window

Glazing stop: The moulding (or part of the window sash) which holds the glass in place

Grill: A bar used to visually separate glass into multiple lites (also named internal grid, muntin bar or window pane divider)

Header: A heavy beam extended across the top of the rough opening to help support the weight of the building

Lite: Glazing framed by muntin bars and/or sash in a window or door

Low-E glass: A commonly used term referring to a low emissivity coating placed on the glass surface to restrict the passage of radiant heat

Moulding: A trim installed around the exterior perimeter of a window frame

Mullion: The connectors installed between individual windows in a multiple unit window

Muntin: A bar used to visually separate glass into multiple lites (also named internal grid, grill or window pane divider)

Operator: A metal arm and gear which allows for easy opening or closing of projecting windows

Pitch: The degree of the slope in a roof

Rails: The horizontal parts of a window sash or door panel

Rough opening: The opening in a wall to accommodate the installation of a window or door

Sash balance: A system of weights or coiled springs which assist in the raising and lowering of single hung and double hung windows

Seat: A wooden board installed on the bottom contour of a bow or bay window (to provide a seat or shelf space)

Shims: Wooden wedges that are used to secure and level windows in the rough opening

Sidelites: Tall and narrow fixed glass on either (or both) sides of an entry door

Sill: The horizontal part that forms the bottom of a window or door frame

Sill course: The row of bricks across the bottom of a rough opening

Simulated divided lite: A method of constructing windows in which grills are attached to the inside and outside of glass panels to simulate the look of true divided lites

Single Hung: A window in which the top sash is fixed (or inoperable) and the bottom sash slides vertically up-and-down for ventilation

Solar gain: The amount of heat which has passed through the glass of windows and doors and has collected inside of the home

Stud: Wood installed vertically and horizontally to build a frame or wall

Transom: A smaller window attached above a door or another window

Triple glazing: A window glazed with three panes of glass (enclosing two separate air spaces)

U-Factor: A measure of heat transmission through a wall or window (the lower the U-Factor, the better the insulating value)

Vapor barrier: A watertight material used to prevent the passage of moisture through floors, walls and ceilings

Venting unit: A window or door that opens or operates

Wind Load: Force exerted on a surface by moving air