Window and Door Glossary

Looking to replace your windows and doors? Our comprehensive glossary of common terms and definitions is here to help! From sashes to glazing, we've got you covered. Gain a better understanding of window and door terminology and make informed decisions for your home improvement project.  

Air Infiltration Industry test that measures the amount of air leakage through a window or door (the lower the number, the better).

Apron A piece of decorative window trim attached to the wall underneath the interior stool (interior sill).

Arch window 4-sided unit with a curve at the top.

Argon Gas An inert, nontoxic gas (denser than air) used between windowpanes to insulate by reducing heat transfer.

Astragal A component fastened to one sash/panel of a gliding window or patio door that becomes the closing shoulder of the operating sash/panel. 

Awning Window Also referred to as a hopper or projected window. Hinged at the top, opens outward from the bottom with a crank, push bar, or manually operated using pressure hinges.

Balance Counter-weight mechanism to assist raising or lowering of a double-hung or single-hung sash. 

Bay Window Window consisting of three or more units that angle out beyond the wall; often configured with a large center unit and two flanking units.

Bottom Rail The bottom horizontal component of a window sash that supports the weight of the glass.

Bow Window A composite of four or more window units in a radial or bow formation.

Brickmould A milled wood trim piece that covers the gap between the window frame and the exterior of the building. On traditional wood windows, the brickmould is nailed through to attach the window to the wall.

High Altitude Capillary Breather Tubes Very small diameter tubes placed within the unit that allows equalization of the air space due to high elevation pressure differences.

Capstock Various materials used to coat wood, vinyl, metal, composite, or other building materials. Provides a durable layer that protects against environmental exposure such as ultraviolet light.

Casement Window A window hinged on either side the sash opens horizontally opposite the hinge.

Casing Brickmould Trim, usually milled wood, attached to the interior wall around a window to cover the space between the window frame and the wall.

Check Rail Located on double-hung windows where the bottom sash and top sash meet, and the lock/keeper is mounted.

Cladding Low maintenance covering or coating attached to the unit exterior to protect it from the elements.

Clear Opening Area The size of the opening created when a unit is in a full open position.

Clerestory Window located up high on wall; typically unreachable from ground level. 

Coil Stock Roll Aluminum that is bent into shape to form a transition piece between the unit exterior and siding/trim. 

Condensation Water that collects as droplets on the glass/sash/panel interior or exterior under certain conditions (typically cold surfaces when exposed to humidity).

Condensation Resistance Condensation Resistance (CR) measures how well a window resists the formation of interior condensation. CR is expressed as a number between 1 and 100. The higher the number, the more resistant to condensation formation.

Conduction The transfer of heat through a solid material, where heat flows to a lower-temperature area from a higher-temperature area.

Convection The transfer of heat through a fluid material such as air due to differences in fluid density and the effects of gravity.

Combination Unit Storm window and insect screen contained in a single frame. 

Cornice An ornamental molding at the top of the window positioned above the exterior trim. 

Cottage Window Double-hung window where the upper sash is shorter than the bottom sash. 

Design Pressure Pressure (measured in pounds per square foot-psf) required by building codes to meet wind load requirements. Our product "PG" Performance Grade rating is used to determine compliance.

Direct Glazed/Direct Set Glass is directly glazed into frame; stationary unit.

Divided Light A window having several small glass panes held in place by muntins within the window sash.

Double Glazing Two panes (or lites) of glass separated by an insulating space in a window or patio door. They may be individual panels or a sealed unit. The dry, airtight space between the panes minimizes condensation and provides excellent insulation properties.

Double-Hung Window Two movable sashes that slide up and down independently.

Dowel Joint A corner joint created by precisely boring matching holes into a door rail and style and joining them together with a dowel pin.

Drip Cap One piece aluminum or vinyl cover installed above windows/doors that directs water away from the top of the unit. 

Dual Pane/Double Pane Glass Two panes of uncoated (non-Low-E) glass with an air-filled cavity (not argon-blend gas-filled).

Egress A window opening providing a secondary means of escape or rescue in an emergency. Check local codes for egress requirements in your area.

Energy Rating Energy performance as affected by the energy efficiency of the framing, weatherstrip, and window glazing. Set by the National Fenestration Rating Council.

ENERGY STAR® Certification Program A government-backed program to help consumers identify energy efficient products. Renewal by Andersen® windows are rated ENERGY STAR qualified.

Equal Lite Window or door with equal spaced grille bars.

Escutcheon Plate Decorative door handle plate that conceals the locking mechanism.

Extension Jamb A wood component fastened to the interior of the window/door that extends the window frame out to the wall depth.

Exterior Trim A decorative trim positioned around the exterior perimeter of a window or door.

Extruded Aluminum Aluminum that is shaped by running it through a die, typically more durable than roll-formed material.

Extrusion The process of forcing heated materials such as aluminum or vinyl through a die to produce specified shapes.

Fenestration Refers to any opening in a structure filled with a window, door, or skylight.

Fibrex® Material An Andersen patented structural composite of wood fiber and PVC polymer that’s two times stronger than vinyl.

Fixed/Stationary Non-venting or non-operable.

Flanker A window set on either or both sides of a center unit (usually a picture unit).

Flashing Water-resistant material that directs water away from your windows. 

Folding Door Door unit with multiple hinging panels that can be folded together to create a large, unobstructed opening.

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 sashes 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 wood side stiles and a tall bottom rail. 

Full Divided Light Grille intended to replicate the look of a true divided light unit; consists of an interior grille, exterior grille, and spacer between the glass panes.

Full-Frame Replacement Replacement method where the entire old window is removed and replaced with a Renewal by Andersen® window.

Fusion Weld A manufacturing process for fusing sash or frame components together. The lineal ends are thermally softened with a hot plate, then welded to form a structural bond. Used in vinyl window manufacture and the manufacture of Renewal by Andersen products.

Gas Fill Gas, typically argon or krypton, is placed between glazing panels to suppress conduction and convection (reduces the U-Factor).

Glass An inorganic material composed of sand (silica), soda (sodium bicarbonate), and lime (calcium carbonate). Also includes small quantities of alumina, boric, or magnesium oxides.

Glass Stop Removable trim piece holding the glass in place on traditional windows. Also referred to as a glazing bead. (Renewal by Andersen uses this only on picture windows.)

Glazing Glass in a window sash or door panel; the act of installing glass in a window sash or door panel.

Glazing Bead A molding or stop around the stiles and rails of the sash which holds the glass in place.

Gliding Door/Sliding Door Door with two or more panels where one panel slides horizontally past another.

Gliding Window/Sliding Window Window with two sashes, where one sash slides horizontally past the other.

Grilles Decorative element that visually divides the glass into a desired pattern. Also called muntins. (Renewal by Andersen offers aluminum grilles between-the-glass (GBG) or wood snap-on grilles (removable) for interior glass surface.)

Gusset Plate Metal plate attached to a window or door to strengthen a window or door joint.

Head Jamb The topmost component of the window or door frame. The window sash seats against it.

Head Track The head member and track along the top of a sliding glass door or gliding window.

Header Heavy beam extended across the top of the rough opening to divert the weight of the wall or roof around the window.

Heat Gain Heat transfer from the outside to the inside of a structure by conduction, convection, and radiation through all surfaces.

Heat Loss Heat transfer from the inside of a house to the outside due to conduction, convection, and radiation through all surfaces.

High-Performance™ Low-E4® Glass Andersen Corporation's brand name for their Low-E (low emissivity) insulated glazing system.

High-Performance™ Low-E4® Sun Glass Andersen Corporation's brand name for a slightly gray-tinted low emissivity glazing system designed for southern climates or windows in rooms where heat buildup (solar heat gain) is a factor.

Infiltration The term used to describe the tendency of a window to allow air or water to move into or out of the building through or around the product's weather stripping or joints. Organizations such as WDMA, AAMA, and NFRC have adopted test standards for measuring acceptable levels of air and water infiltration for specific grades of product performance.

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

Insert Replacement Window replacement method where a complete frame/sash unit is inserted inside the jamb area (pocket) of the original window frame.

Inside Stop On an older wood window, a piece of wood trim attached to each side jamb that defines the inner edge for the lower sash channel.

Installation Flange A fin of vinyl or metal that extends outward perpendicular from the frame of a window, which allows the window to be suspended within a rough opening.

Insulating Glass Two or more pieces of glass with a space between them that are hermetically sealed to provide insulating characteristics.

Insulation Any type of material used to prevent the passage of heat, cold, fire, or noise.

Interlock The place where a mechanism of one panel/sash connects tightly with the corresponding mechanism of an adjacent panel/sash, as in patio doors, gliding and double-hung windows.

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

Jamb Cover (Liner) Material used to trim off visible surfaces on windows and doors. Often used to create travel channels and weatherstrip shoulders; can hide and protect functional hardware such as double-hung balancers.

Keeper The hardware piece where the lock engages on the sash.

Laminated Glass A type of safety glass; two or more sheets of glass with an inner layer of plastic which holds the glass pieces if the glass is broken.

Lift The handle attached to the rail on a double hung or gliding window.

Light (Lite) Individual glass panes within a window sash or door panel.

Lineal Long length of extruded window material; includes wood, aluminum, vinyl, or Fibrex composite extrusions.

Low-E Abbreviation for low emissivity, a glass coating process that allows most of the sun's visible spectrum to pass through to the interior and reflects most heat energy back to its source (in cold weather, a low-E coating reflects radiant energy back into the house; in hot weather, it reflects the sun's heat energy back to the outside). A variety of low-E coatings are offered by glass manufacturers, with varying degrees of efficiency.

Meeting Rails The two horizontal members of a double-hung sash that meet and are locked together when the window is closed. Also called check rail.

Meeting Stile Either vertical-edge member in a pair of gliding window sash or door panel that meet and lock when the sash/panel are closed. Comparable to the meeting rail on a double-hung window.

Miter A method of cutting and joining two pieces of trim. The edge of a material beveled to make a miter joint; usually at a 45-degree angle.

Mortise and Tenon Strong wood joint made by fitting together a slot (mortise) in one board and the matching projecting member (tenon) on the adjoining board.

Mullion/Mull A member between two separate windows being attached together. May be vertical or horizontal, structural or integral.

Mull Post/Muntin A strip of wood or metal separating and holding panes of glass in a window.

NFRC National Fenestration Rating Council is a non-profit organization that provides fair, accurate and credible energy performance ratings for windows, doors, and skylights.

Obscure Glass Glass with a texture of pattern of various degrees of opacity that limits visibility through a window or door for privacy, light diffusion, or decoration (frosted, etched, etc.).

Operable Window Window that can be opened and closed.

Operator A device for opening and closing windows. Usually refers to a crank-operated mechanism found on casement and awning windows.

Outside Stop On an older wood window, a piece of external wood trim attached to each side jamb that defines the outer edge for the upper sash channel. Also called blind stop.

Pane A sheet of glass; a compartment in a door or window containing a sheet of glass.

Panel A sliding or fixed unit consisting of a frame containing a light of glass.

Panning A type of metal flashing system used under the door or windowsill to channel water away from the framing and siding.

Parting Stop A narrow strip that separates and secures two sashes in the window frame. It provides a channel in which the sash can move.

Passive A sash that can be operated if necessary but usually is not, e.g., the left-hand sash of a gliding window.

Perma-Shield^® Andersen Corporation's trademark name for a system of products that provides next-to-no maintenance through vinyl wrapping of wood, high-durability paint finishes, and other techniques. It originally referred to Andersen's use of the process for extruding a vinyl sheath completely around a wood component.

Picture Window Fixed window with no opening sash.

Plumb Vertically straight up/down. As an installation term, it refers to the importance of making sure that the window sides are perfectly perpendicular to the earth.

Profile The end view shape of a lineal piece of the extruded or milled material.

R-Value A measure of resistance to heat flow; a higher value indicates better heat-insulating property.

Rail Horizontal member of a window sash or door panel. There are four rails on a double-hung window: the bottom rail, two meeting rails or check rails, and the top rail.

Rough Opening The opening in a wall where a window or door will be installed.

Safety Glass Also called tempered or wire-mesh glass, it meets a variety of industry and government safety standards.

Sash Lock The lock that connects with the keeper. Used on double-hung, casement, awning, and gliding windows.

Sash Pack A window replacement system using a sash and jamb liner components applied to an existing window frame.

Sealant Various materials used to seal openings or junctions between parts. May be liquid or solid, depending upon the application.

Shim A wedge often made of wood used to plumb and/or level a window or door in the rough opening. Shims are also used to adjust hardware positioning. The term is also used to describe the action of bringing to a level by inserting a shim.

Side Jamb The left and right sides of the window frame.

Sill Angle Slope of the outside windowsill.

Simulated Divided Lights A single unit of insulating glass with a simulated grille installed on the glass surface or between the glass panes that gives the appearance of small panes separated by muntins.

Simulated True Divided Light A single unit of insulating glass with three sets of grilles: on the exterior and interior surfaces, and between the glass panes.

Single-Hung A variation of the double-hung window style where the upper sash does not operate. Typically, less expensive than a true double-hung window.

Sliding Glass Door A door fitted with two or more panels that move horizontally on a track or in grooves.

Solar Heat Gain Coefficient (SHGC) A measurement of the sun's heat energy that passes through the window/door. The lower the value the less heat gain through the product.

Stationary A glazed sash or panel that cannot be operated.

Stile The vertical-edge framing components of a window sash.

Stool The interior window trim applied horizontally at 90 degrees to the wall at the base of a window (normally double hung), commonly called the windowsill.

Stop A trim member attached to the window or door intended to hold, position, or separate components.

Storm Door A seasonal second door installed in front of an exterior access door to provide additional insulation or protection from bad weather and allow ventilation.

Storm Window A seasonal second window installed on the outside or inside of a window to provide additional insulation or protection from bad weather and allow ventilation.

Tempered Glass Treated glass strengthened by reheating and then sudden cooling; up to four times stronger than normal glass. (See Safety Glass.)

Thermal Break An element (space or other material) placed between other elements to reduce conduction. (Andersen uses a vinyl thermal break on patio door sills.)

Thermal Conductivity Refers to a physical property that affects the extent to which heat or cold is transferred by a material. For example: aluminum has 1,000 times the thermal conductivity of Fibrex™ material, making it a far more efficient insulating window material.

Thermal Expansion A term that describes the expansion a material exhibits when exposed to high temperature, or the shrinkage (contraction) that results when exposed to low temperatures.

Threshold Decorative wood component used as a transition door sill to the interior flooring.

Tilt-Wash Double-hung window design that pivots or tilts for ease of cleaning.

Tinted Glass Glass that is colored using a mineral admixture; sometimes a silver coating applied to the glass surface. Used to reduce radiation transmission.

Transom A crosspiece separating a door from a window above it.

Transom WindowA window positioned directly above another window or door.

Triple Glazing Three panes with two air spaces between.

TruScene® Insect Screen A nearly invisible micro-fine stainless steel mesh insect screen that is one-third the diameter of a standard screen wire and allows over 50% more clarity than an Andersen conventional insect screen.

U-Factor Commonly used measurement of heat transmission through a window/door. The lower the U-Factor, the better the insulating value.

Ultraviolet Light (UV) Invisible rays of the spectrum at its short-wavelength violet end; the invisible solar radiation that can cause heat buildup and fading of wood, fabrics, and other surfaces. (Low-E coatings are added to window glazing to moderate or eliminate harmful undesired UV wavelengths of light.)

United Inch Term used to describe a method of calculating the size of a window, by adding the height to the width and expressing the sum in inches. Used for price estimating.

Unit Dimension (UD) The UD is the precise size of the window (unit) when measured in width and height from the outermost edge of the window frame, not including any installation flange or brickmould.

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

WDMA Organization established by window and door manufacturers to create industry standards and advocate self-monitoring.

Weatherstripping A narrow strip of material placed between window sash or door panels and frame to keep out rain, air, etc. May take many different forms, depending on product design and usage.

Welding The fusing or melting together of two or more individual components to form a solid bond. For example, Renewal by Andersen window sash stile and rails, and many frame components are welded together.

Window Hardware Mechanical devices and attaching hardware such as locks, hinges, pivots, catches, lifts and pulls, and stays.