Window Glossary

The following is a list of common window terms to help you in your quest of researching windows.


AAMA - American Architectural Manufacturers Association. Source of performance standards, product certifications and educational programs for the window, door, storefront, curtain wall, and skylight industries.

Air Infiltration - The amount of air that passes between a window sash and frame.

Argon Gas - An inert, nontoxic gas used in insulating glass units to reduce heat transfer.

Awning Window - Similar to a casement except the sash is hinged at the top and swings out.


Balance – A mechanical device used in a single and double-hung windows that provides force to the bottom half of the window as a means of counterbalancing the weight of the sash to provide for an easy opening and closing.

Bay Window – An arrangement of three or more window units (usually with a large center unit and two flanking units) that project from the building at 30°, 45°, or 90° angles.

Bead – A narrow wood strip against which a swinging sash closes.

Bow Window – A composite of four or more window units that projects from the wall in an arc or bow formation.


Casement – A window sash that is hinged usually on one side. In-swinging are French in origin; Out-swinging are England in origin.

Casing – Exposed molding or framing around a window or door. Used to cover the space between the window frame and the wall.

Composite Frame – A frame consisting of two or more materials.

Condensation – A process of moist air forming on the interior of a glass window.

Conduction – Heat transfer (higher-temperature area to lower-temperature area) though solid material.

Convection – Transport of heat and moisture by the movement of a fluid.


Double-Glazing – Two panes of glass in a window that increase energy efficiency, improve insulation, and provide other performance benefits.

Double-Hung Window – A window consisting of two sashes in which both the upper and lower sashes move up and down.


Eyebrow Window – A small, horizontally rectangular window, often located on the top molding of the house, aligned with the windows below.


Fanlight – A semi-circular window over a door or window, with radiating bars suggesting a fan.

Fiberglass – A composite material made by embedding glass fibers in a polymer matrix.

Fixed Light – A sheet of glass installed directly into non-operating frame.

Fixed Panel – An inoperable panel of a sliding glass door or slider window.

Fixed Window – A window with no operating sashes.

Frame – Fixed frame of a window that holds the sash or casement.


Gas Fill – A gas other than air, usually argon or krypton, placed between window glazing panes to reduce the U-Factor by suppressing conduction and convection.

Glazing – The glass panes or lights in the sash of a window.

Greenhouse Window – A three-dimensional window that projects from the exterior wall and usually has glazing on all sides except the bottom, which serves as a shelf.


Header – The upper-horizontal member of a window frame.

Heat Gain – The amount of heat gained from direct sunlight by means of conduction, convection, and radiation through all surfaces of the house.

Heat Loss – The amount of heat lost from inside to outside by means of conduction, convection, and radiation through all surfaces of the house.

Hinged Window – A window with an operating sash that has hinges on one side.

Hopper Window – A window that contains a single sash that tilts inward.

Horizontal Slider – A window with a movable panel that slides horizontally.


Insulating Glass – Also known as Double Glazing. Two or more pieces of glass spaced apart and hermetically sealed to form a single glazed unit with one or more air spaces in between.

Insulation – Construction materials used for protection from noise, hear or cold.


Krypton Gas – An inert, nontoxic gas used in insulating windows to reduce heat transfer.


Laminated Glass – Two or more sheets of glass with an inner layer of transparent plastic to which the glass adheres if broken; prevents from shattering.

Low-E – Virtually invisible metallic coating used to reflect heat back to its source. It is applied as a thing coat on the panes of glass


Meeting Rail – The part of a sliding glass door, a sliding window, or a hung window where two panels meet and create a weather barrier.

Metal-Clad Windows – Exterior wood parts covered with metal to deter the elements.


New-Construction Windows – Windows used for new structures or additions to old structures.


Obscure Glass – Any textured glass such as frosted, fluted, ground, etc which is used for privacy, light diffusion, or decorative effects.

Operable Window – Window which can be opened.


Pane – A sheet of glass.

Panel – A component of a sliding glass door. A panel may be sliding or fixed.

Panning – Outside trim that which extends around the perimeter of a window opening and is used to cover up the old window material.

Picture Window – A large, fixed window that is usually longer horizontally than vertically to provide a panoramic view.

Pivot Window – A window that opens by pivot points between the sash and frame.

Projected Window – A window fitted with one or more sashes on pivoted arms or hinges.


R-Value – A measure of a material’s resistance to the passage of heat. The higher the R-Value, the greater the insulation power.

Radiation – The transfer of energy or heat in the form of electromagnetic waves from one surface to another.

Rail – Horizontal member of a window sash.

Reflective Glass – Window glass coated so as to reflect radiation striking its surface.

Replacement Window – Used to replace most, but not all, elements of an existing window.

Retrofitting – Adding or replacing items on existing buildings.

Rough Opening – The opening in a wall into which a door or window is to be installed


Safety Glass – Also known as laminated or tempered glass. Glass that is treated to prevent injury in the event it is broken.

Sash – A framework that holds the panes of a window in the window frame.

Screen – Used to keep insects from passing though the open window.

Sealant – Liquids, pastes, or coatings used to seal edges of window frames. Provides protection against water leaks.

Sill – The lowest horizontal member in a door, window, or sash frame.

Single Glazing – Single pane of glass in a window or door. Not as energy-efficient as double glazing.

Single-Hung Window – A window with only one sash that moves up and down. Usually, the lower one is movable, the upper one is stationary.

Sliding Glass Door – A door with one or more panels which slide or roll horizontally on a track.

Sliding Window – A window in which the sashes more horizontally.

Solar Control Coating – Thin film coatings on glass that help absorb or reflect solar energy. Reduces solar gain.

Solar Radiation – Radiation emitted by the sun – includes ultraviolet and infrared wave lengths as well as visible light.

Stile – A vertical side member of a window sash or door panel.


Tempered Glass – Heat strengthened glass used for safety purposes. When broken, it shatters into small pieces to protect from injury.

Thermal Break – Material used to lessen the transfer of heat from one component to another.

Thermal Expansion – The increase in the dimension or volume of a material due to temperature change.

Tilt Window – A window in which the sash can be tilted into the room for interior washability and ventilation.

Tinted Glass – Glass to which a small amount of color has been added consistently throughout the glass. Any tinting reduces both visual and radiant transmittance.

Transmittance – The percentage of radiation that can pass though glazing.

Triple Glazing – Three panes of glass with two air spaces between.


U-Factor (U-Value) – Measure of heat flow though a material. The lower the U-Factor, the greater a window’s resistance to heat flow and the better its insulating value.

UBC – Uniform Building Code.

UV (Ultraviolet Light) – Electromagnetic radiation in the range of 300 to 400 nanometers. UV radiation is not visible, but can cause fading of paint finishes, furniture, and fabrics.


Vinyl – Polyvinyl chloride material, which is durable and resilient. Very easy to clean.

Vinyl-Clad Window – A window with exterior wood parts covered with vinyl.


Weather-Stripping – Material used to form a weather-resistant seal around an operable sash.

Window Hardware – Various devices and mechanisms for the window. Includes catches, hinges, pivots, sash weights, etc.

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