Window and door terminology

The window and door industry has a lot of specific words and expressions. It is sometimes difficult to understand what they really mean! Take the time to understand our jargon by visiting this section.

Window and door terminology

Arch or camber window: 4 sided unit with a curve at the top


Assembly: Single units mulled together.


Awning window: Unit with hinged sash that swings outward from the bottom; allows ventilation at the bottom


Bow Windows: A series of adjoining window units, installed on a radius.

Brickmould: An exterior moulding of window and door frames that  casing serves as the boundary  for brick or other siding material.

Cam Lock: A lever operated lock which is used to prevent intrusion through the sash.

Casement window: Unit with hinged sash that opens to the side; allows top to bottom ventilation

Cladding: Low maintenance covering or coating attached to the unit exterior


Egress window: A venting window required by buiding codes for emergency escape and rescue, which are typically required in bedrooms and which are required to meet certain minimum opening dimensions.

Extruded aluminum: Aluminum that is shaped by running it through a dye, typically more durable than roll-formed material

Extrusion: An article or product of vinyl or metal-made by the process of extruding.


Fixed/Stationary: Non-venting or non-operable

Flanker: A term used to describe a side or lateral part of an assembly window.

Foot lock: Auxiliary lock used on gliding doors to secure the operating panel to the sill

Frame: Outer structure of a window or door that holds the sash or panel in position

French casement window: Unit with two venting sash that open outward to provide a large center opening with no center post

French door: Hinged door(s) with large glass area surrounded by a wide side stiles and rails


Grilles: Grille bars that are placed between the glass panes; allows for easy cleaning

Half Round: Half circle unit consisting of a curved top and linear bottom

Insert window: A new window unit intended to be installed inside the frame pocket of an existing window

Insulating glass unit: Two or more glass panes that are sealed together to increase energy efficiency


Jamb: Window or door frame members that form the top and sides of a unit

J-channel: Receiver components that surrounds a window intended to hide the seam between the window and siding

Lite: Individual glass panes within a window sash or door panel


Mulling: Joining of two or more window or door units together; joint can run vertically, horizontally or both

Multi-point lock: Lock that engages the sash or panel in multiple locations; activated by a single motion

Nailing flange / Installation flange: Narrow attachment strip on the window perimeter that typically used to secure the window to the rough opening

Operator: An operating sash, panel or unit, also the metal arm, gear and handle used to open and close hinged windows

Oriel or Cottage window: Single- or Double-hung window where the upper sash is shorter than the bottom sash

Palladian window: Large, arch-top window flanked by smaller windows on each side

Panel: Refers to the rail, stile and glass assembly on a door; similar to a window sash

Rail: Horizontal components of a window sash or door panel framework

Rough opening: Opening in a wall for the installation of a window or door.  The rough opening is larger than the actual unit to allow for shimming and insulating.

Round Top: Generally a semicircle window which is mulled to the top of another window or door, thus forming the round top appearance. There are full round tops, separated round tops, ellipticals, transoms, inverted corners, ovals and Gothic heads, etc. Round tops can be used separately or combined with other units to create a seemingly endless selection.

Sash: The operating and/or stationary portion of the window unit that is separate from the frame. The sash consists of the following parts

Screen: A tightly woven mesh attached to a frame; allows outside air ventilation while keeping insects out

Sidelite: A stationary glass panel mulled to or installed next to a door.

Sill: Horizontal member that forms the bottom of a window or door frame

Simulated divided light: Use of interior and exterior grille to simulate the look of a window with multiple glass lites

Single Hung: A window with a fixed upper sash and lower moveable sash that slides vertically in a single frame 

Slider: Horizontal operating units which have one sash fixed while the other glides open and shut horizontally.

Sliding patio door: Door with two or more panels where one panel slides horizontally past another

Spacer: Used to separate the two pieces of glass in an insulating glass panel.

Stile: The vertical components of a window sash or door panel

Threshold: transition door sill to the interior flooring

Transom: A window above a window or door. Transoms can be either stationary or operating.

Triple pane: Glass construction consisting of three distinct layers of glass and two air-spaces

Weather-Stripping: A strip of resilient material designed to seal the sash and frame members in order to reduce air and water infiltration.

Weep holes: Small holes placed on the exterior of a window or door that allows for water drainage