AAMA: American Architectural Manufacturers Association, a national trade association that establishes voluntary standards for the window, door, and skylight industry.

Acrylic: Thermoplastic glazing material.

Aerogel: A microporous, transparent silicate foam currently under development for potential use as a glazing cavity fill material, offering very high thermal performance.

Air infiltration: The amount of air leaking in and out of a building through cracks in walls, windows, and doors.

Airspacer: Component placed at the perimeter of an insulating glass unit to separate the two lites of glass.

ANSI: American National Standards Institute, a clearinghouse organization for all types of standards and product specifications.

Annealed glass: Standard float glass.

Arch-top: One of several terms used for a variety of window units with one or more curved frame members, often used over another window or door opening. Also referred to as circle-heads, circle-tops, round-tops.

Argon: An inert, nontoxic gas used in insulating glass to reduce heat transfer.

ASHRAE: American Society of Heating, Refrigeration, and Air Conditioning Engineers, a national association that establishes standards for building energy performance.

Astragal: Center post between two swinging doors.

ASTM: Formerly the American Society for Testing and Materials, and now officially ASTM International, this organization establishes material standards (including glass) and test methods addressing a broad spectrum of industries. It has also produced a window installation standard.

Awning: Window with sash swinging outward from bottom.

Backbedding: Material or compound used to seal the glass to a window sash.

Balance: Mechanical device (normally spring loaded) used in single- and double-hung windows as a means of counterbalancing the weight of the sash during opening and closing.

Bay: A combination of window units which projects to the exterior. Usually features a large center unit with two flanking units at 30° or 45° angles to the wall.

Bottom rail: The bottom horizontal member of a window sash or door panel.

Bow: A combination window which projects to the exterior. Usually features four or more window units in a radial or bow formation.

Box bay: A combination of window units which projects to the exterior. Usually features a large center unit with two flanking units at 90° angles to the wall.

Breather tube: Tube placed through airspacer and seal of insulating glass which allows unit to accommodate changes in pressure between time and location of manufacture and time and location of installation, where it is sealed. Usually used to accommodate changes in altitude between plant and jobsite.

Brickmould: A type of external casing for windows and doors.

Casement: Window with sash cranking outward, to the right or left.

Casing: Exposed moulding or profile around a window or door, on either the inside or outside, to cover the space between the window frame or door jamb and the wall.

Caulking: A compound for filling joints and sealing cracks to prevent leakage of water and air.

Cellular PVC: Extruded polyvinyl chloride material used in window and door components and trim. Unlike rigid (or hollow) vinyl, it features a foam or cell-structure inside. It can often be nailed, sawn, and fabricated like wood.

Cellulosic Composite: Generally, a material combining an organic material, such as wood fiber, extruded with a plastic.

Check rail: The bottom rail on the upper sash and the upper rail of the lower sash of a double-hung window unit, where the lock is mounted. Also referred to as a meeting rail.

Circle-top: One of several terms used for a variety of window units with one or more curved frame members, often used over another window or door opening. Also referred to as arch-tops, circle-heads, round-tops.

Cladding: Material placed on the exterior of wood frame and sash components to provide ease of maintenance. Common cladding materials include vinyl and extruded or roll-formed aluminum.

Clerestory: A window in the upper part of a high-ceilinged room that admits light to the center of the room.

Combination door: A screen or storm door used in combination with a primary door. Storm windows are also referred to as combination windows.

Composite: A term used for window or door components which consist of two or more materials, such as wood and plastic. The term is also used for windows and doors which combine two or more materials in the frame or sash construction, such as a product with a wood interior and a vinyl or aluminum exterior.

Condensation: Water vapor from the air deposited on any cold surface which has a temperature below the dew point. Sometimes a problem on cold (and poorly insulated) window glass or framing that is exposed to humid indoor air.

Corner cleaner: Machine which removes the bead of excess material formed in welding vinyl window corners.

CRF: Condensation Resistance Factor. A rating of a window's ability to resist condensation. The higher the CRF, the less likely condensation is to occur.

Dade County: Florida county, including Miami, which has set numerous standards and requirements for hurricane-resistant windows and doors.

Desiccant: A material used to absorb moisture from within the sealed airspace of an insulating glass unit.

Design pressure (DP): A measurement of the structural performance of a window or door. Usually specified as one-and-half times greater than necessary based on expected building wind and weather conditions.

Divided lites: Separately framed pieces or panes of glass. A double-hung window, for instance, often has several lites divided by muntins in each sash. These designs are often referred to as six-over-six, eight-over-one, etc., to indicate the number of lites in each sash. Designs simulating the appearance of separately-framed panes of glass are often referred to as SDLs or simulated divided lites. Designs using actual separate pieces of glass are sometimes referred to as TDLs or true divided lites.

Dormer: An area which protrudes from the roof of a house, generally featuring one or more windows.

Double glazing: Use of two panes of glass in a window to increase energy efficiency and provide other performance benefits. May or may not refer to an insulating glass unit.

Double-hung window: Window featuring two operable sash which move vertically in the frame.

Double-strength glass: Glass between 0.115 and 0.133 inches thick.

Drip cap: Moulding placed on top of the header brickmould or casing of a window frame.

Edge effect: Heat transfer at the edge of an insulating glass unit due to the thermal properties of spacers and sealants.

Electrochromic glazing: Glass or other glazing material that can be switched from clear to opaque electronically.

Egress window: Window designed to be large enough for a firefighter to climb in or a person to climb out in an emergency. U.S. building codes require each bedroom of a home to have an emergency exit window, with minimum sizes specified.

Energy Star: A program sponsored by the U.S. Department of Energy which establishes minimum performance standards for windows to be recognized as energy efficient. Three different sets of standards for U-value and solar heat gain have been established for three different climate zones in the U.S.

Extension jamb: A trim component which extends from the interior of the window frame to the interior wall.

Extrusion: The process, in which a heated material is forced through a die, used to produce aluminum, vinyl (PVC), and other profiles or components used in the production of windows and doors. Term is also used to refer to the profiles or lineals manufactured by this process and used to make window and door components.

Fanlight: A half-circle window over a door or window with radiating bars.

Fogging: A deposit or film left on an interior surface of a sealed insulating glass unit due to extreme conditions or failed seals.

Fenestration: Originally, an architectural term for the arrangement of windows, doors, and other glazed areas in a wall. Has evolved to become a standard industry term for windows, doors, skylights, and other glazed building openings. From the Latin word, "fenestra," meaning window.

Finger-Joint: A toothed joint used to combine to pieces of wood end to end.

Fixed lite: Non-venting or non-operable window.

Fixed panel: Non-operable door usually combined with operable door unit.

Flashing: A thin strip of metal or other material that diverts water away from
a window, door, or skylight.

Float glass: Glass produced by a process in which the ribbon is floated across a bath of molten tin. The vast majority of flat glass is now produced using this method. The terms "plate" glass and "sheet" glass refer to older manufacturing methods still in limited use.

Flush door: Door produced using two skins or faces separated by a stile-and-rail frame construction at the perimeter. Flush doors may produced with a hollow core or solid core.

French door: Generally refers to a pair of hinged doors which open from the middle. Also incorporates wider stile and rail components around the glass than typical glazed doors.

Fusion-weld: A term used for a type of corner construction, used with vinyl and other types of windows and doors, in which a small amount of material on the ends of two pieces are melted or softened, then pushed together to form a single piece. This is also referred to simply as a welded corner.

Glazing: Glass (and other materials) in a window or door. Also, the act or process of fitting a unit with glass.

Glazing stop: A component of the sash or door panel which holds the glass in place.

Glider: A window with a movable sash that slides horizontally. Also referred to as a horizontal sliding window.

Grille: A term referring to window pane dividers or muntins. It may be a type of assembly fitted to the interior of the window or door unit which can be detached for cleaning. Also can be fitted inside the sealed insulating glass unit, when it is also referred to as a grid.

Hard-coat glass: A glass product that is coated during the manufacturing process at the molten glass stage. Also known as a pyrolytic coating, this type of coating offers a surface that is as generally as durable as an ordinary glass surface, and therefore requires no special handling and does not to be used in an insulating glass unit. The other type of glass coating is a sputter-coat, which is applied in a secondary process. Sometimes referred to as a soft-coat, these types of coatings generally require some additional care in handling and fabrication and must be used within an insulating glass unit.

Head: Main horizontal frame member at the top of a window or door.

Header: Horizontal framing member placed over the rough opening of a window or door to prevent the weight of wall or roof from resting on the frame. Also known as a lintel.

Heat gain: The transfer of heat from outside to inside by means of conduction, convection, and radiation through all surfaces of a house.

Heat loss: The transfer of heat from inside to outside by means of conduction, convection, and radiation through all surfaces of a house.

Hollow-core door: Flush door constructed with two skins or door faces separated by stiles and rails at the perimeter. Generally a honeycomb type support is used inside the door between the two faces.

Hopper: Window with sash that swings inward from the top.

Horizontal slider: A window with a movable sash that slides horizontally. Also referred to as a gliding window.

IBC: International Building Code. Published by the International Code Council, the IBC primarily covers nonresidential construction.

IECC: International Energy Conservation Code. Published by the International Code Council, the IEEC sets forth compliance methods for energy efficient construction of both residential and nonresidential construction.

Insulating glass (IG): Two or more lites of glass with a hermetically sealed airspace between the lites. The sealed space may contain air or be filled with an inert gas, such as argon.

IRC: International Residential Code. Published by the International Code Council, the IBC primarily covers low-rise residential construction.

Jalousie: Window made up of horizontally-mounted glass louvers or slats that abut each other tightly when closed and rotate outward when cranked open.

Jamb: Main vertical members forming the sides of a window or door frame.

Jambliner: The track installed inside the jambs of a double-hung window, on which the window sash slide.

KD (Knocked down): Unassembled window or door.

Laminated glass: Two or more sheets of glass with an inner layer of transparent plastic to which the glass adheres if broken. Used for enhanced safety and security, as well as sound reduction.

Lineal: A standard length profile or shape which is cut and processed to make window and door components.

Lintel: A structural component or beam above a window or door opening that supports the wall above. Also referred to as a header.

Lite: A piece of glass. In windows and doors, refers to separately framed panes of glass (as well as designs simulating the look of separately framed pieces of glass). Sometimes spelled "light."

Low-emissivity (Low-E) glass: A coated glass product which reflects heat.

Masonry opening: Area in a masonry wall left open for windows or door.

MDF: Medium-density fiberboard. A wood-fiber composite used in a variety of window, door, and millwork applications.

MEC: Model Energy Code, established by Energy Policy Act of 1992 to serve as baseline for state energy codes. Succeeded by International Energy Conservation Code (IECC).

Mechanical window: A term for a product, usually vinyl, in which the corners are assembled using screws or other fastening mechanisms, as opposed to a welded corner construction. Also referred to as a mechanically-fastened window.

Mullion: A component used to structurally join two window or door units.

Multipoint lock: A locking system, operated with one handle, which secures a window or door at two or more locking points.

Muntin: Profile or moulding, either vertical or horizontal, used to separate glass in a sash into multiple lites. Generally refers to components used to construct divided lite grids or grilles simulating a divided lite look.

Nailing fin: An accessory component or integral extension of a window or patio door frame which generally laps over the conventional stud construction and through which nails are driven to secure the frame in place.

NFRC: National Fenestration Rating Council. A body which has established methods for rating and certifying the energy performance of windows.

NWWDA: National Wood Window and Door Association. Trade organization which has established many standards related to wood window and door products. It is now the Window and Door Manufacturers Association (WDMA). One-step distributor: An industry term for a wholesale company which which buys building products from a manufacturer and sells them to builders, contractors, and homeowners is referred to as a one-step distributor. A wholesaler which buys building products from the manufacturer and sells them to lumber yards and home centers, which in turn sell to builders, contractors, and homeowners is referred to as a two-step distributor.

Oriel: Window style in which the upper sash is larger than the lower sash.

Palladian: A large, arch-top window flanked by smaller windows on each side.

Panel: Component, usually wood, mounted within stile and rail members of door. Also used to refer to entire door.

Panning: In replacement window work, the outside aluminum trim that can extend around the perimeter of the window opening; used to cover up the old window material.

Parting stop: A narrow moulding, either integral or applied, that holds a sash or panel in position in a frame.

Picture window: Large, non-operating window. It is usually longer than it is wide to provide a panoramic view.

Pivot window: A unit with a sash that swings open or shut by revolving on pivots at either side of the sash or at top and bottom.

Polycarbonate: A plastic material used for glazing.

Polyvinyl Butyral (PVB): Plastic material used as the interlayer in the construction of some types of laminated glass.

Plate glass: Flat glass produced by grinding and polishing to create parallel plane surfaces affording excellent vision. Although the term is still used commonly, most window glass is now produced using the float process. See float glass.

Pre-hanger: A company which buys doors, framing, hardware, glass lites, and other components, and prepares (or pre-hangs) the unit for installation.

Prime window: A primary window, as opposed to a storm or combination unit added on.

Projected window: A window in which the sash opens on hinges or pivots. Refers to casements, awnings, and hoppers.

Pultrusion: The process used to produce fiberglass composite profile or component used for the production of windows and doors. Term is also used generally to refer to the composite profiles or lineals cut and processed to make window and door components.

PVC: Polyvinylchloride. An extruded material used for window and door framing.

Pyrolytic glass: A glass product that is coated, usually to provide low-emissivity or solar control benefits, during the manufacturing process at the molten glass stage. Commonly referred to as a hard coat, this type of coating offers a surface that is as generally as durable as an ordinary glass surface, and therefore requires no special handling and does not need to be used in an insulating glass unit. The other type of glass coating is a sputter-coat, which is applied in a secondary process. Sometimes referred to as a soft-coat, these types of coatings generally require some additional care in handling and fabrication and must be used within an insulating glass unit.

Radiation: The transfer of heat in the form of electromagnetic waves from one separate surface to another. Low-E glass is designed to reduce this type of heat transfer by reflecting electromagnetic waves.

Rail: Horizontal member of the framework of a window sash or door.

Reflective glass: Window glass coated to reflect visible light and solar radiation striking the surface of the glass.

Roof window: An operable unit similar to a skylight placed in the sloping surface of a roof.

Rough opening: Framed opening in a wall into which a window or door unit is to be installed.

Round-top: One of several terms used for a variety of window units with one or more curved frame members, often used over another window or door opening. Also referred to as arch-tops, circle-tops, and circle-heads.

R-value: Resistance to thermal transfer or heat flow. Higher R-value numbers indicate greater insulating value. R-value is frequently used by insulation industry and is the recipricol of U-value, a value more generally used in the window industry.

Safety glass: A strengthened or reinforced glass that is less subject to breakage or splintering and less likely to cause injury if broken. Law requires glass in doors to be some type of safety glazing product, such as tempered or laminated glass.

Sash: An assembly of stiles and rails (vertical and horizontal members) made into a frame for holding glass.

Sash cord: Rope or chain in double-hung windows which attaches the sash to the counter balance.

Sash lift: Protruding or recessed handle on the inside bottom rail of the lower sash on a double- or single-hung window.

Sash weights: Concealed cast-iron weights used to counterbalance the sash of older double-hung windows.

Self-cleaning glass: Glass treated with a special coating. Currently, commercially available products feature a coating that uses the sun's UV rays to break down organic dirt through what is called a photocatalytic effect. The coating also provides a hydrophilic effect, which reduces the surface tension of water to cause it to sheet down the surface easily and wash away dirt.

Shading coefficient (SC): A measure a window's ability to transmit solar heat, relative to that ability for 1/8-inch clear glass. The lower a unit's shading coefficient, the less solar heat it transmits, and the greater its shading ability. It is being phased out in favor of the solar heat gain coefficient (SHGC).

Sheet glass: A transparent, flat glass found in older windows, now largely replaced by float glass.

Sidelites: Narrow fixed units mulled or joined to operating door units to give a more open appearance.

Sill: The main horizontal member forming the bottom of the frame of a window or door.

Simulated divided lites (SDLs): A type of grille or grid design that creates the appearance of a number of smaller panes of glass separated by muntins, but actually uses larger lites of glass with the muntins placed between and/or on the surfaces of the glass layers.

Single glazing: Use of single lite of glass in a window. Generally not as energy efficient as insulating glass or other forms of double glazing.

Single-hung: A window resembling a double-hung, or vertically sliding window, with a fixed top sash.

Single-strength glass: Glass with thickness between 0.085 and 0.100 inches.

Skin: A single piece of material used as the face of a door.

Slab: A term for a complete door panel that has not been prepared for installation into a frame.

Smart window: Generic term, sometimes used for windows offering high energy efficiency or windows featuring switchable glass to control solar gain.

Solar control glass: Glass produced with a coating or tint that absorbs or reflects solar energy, thereby reducing solar gain.

Solar heat gain coefficient (SHGC): A rating, which is now generally replacing shading coefficient, measuring a window's ability to transmit solar heat. It measures both the solar radiation which is directly transmitted, as well as the solar radiation absorbed by the glass and subsequently transmitted. The lower a unit's solar heat gain coefficient, the less solar heat it transmits, and the greater is its shading ability. It is approximately equal to the the shading coefficient divided by 1.15. It is expressed as a number without units between 0 and 1.

Solid-core door: Flush door produced with a solid material placed within the door skins.

Soft-coat glass: A glass product that is coated in a secondary process known as sputter coating, usually to offer low-emissivity or solar control benefits. The term refers to the fact that these types of coatings generally require some additional care in handling and fabrication and must be used within an insulating glass unit. A hard-coat or pyrolytic glass is coated during the manufacturing process at the molten glass stage. This type of coating offers a surface that is as generally as durable as an ordinary glass surface, and therefore requires no special handling and does not to be used in an insulating glass unit.

Sound Transmission Class (STC): A rating measuring a window's acoustic properties or its ability to reduce sound transmission. An STC rating is determined by measuring the sound transmission over a selected range of sound frequencies. The higher the number, the less sound transmitted.

Spectrally selective glass: A coated or tinted glazing with optical properties that are transparent to some wavelengths of energy and reflective to others. Typically spectrally selective coatings are designed to allow high levels of visible light or daylight into a building and reflect short-wave and long-wave infrared radiation.

Sputter-coating: A secondary manufacturing process in which a thin layer of materials, usually designed to offer low-emissivity or solar control benefits, is applied to glass. Sputter-coatings are commonly referred to as soft-coats, as they generally require some additional care in handling and fabrication and must be used within an insulating glass unit. A hard-coat or pyrolytic glass is coated during the manufacturing process at the molten glass stage. This type of coating offers a surface that is generally as durable as an ordinary glass surface, and therefore requires no special handling and does not to be used in an insulating glass unit.

Stile: The main vertical frame members of a sash or door.

Stile-and-rail door: Traditional type of wood door constructed with vertical stiles and rails with openings filled with raised wood panels or glass.

Stool: Interior trim piece sometime used to extend a window sill and act as a narrow shelf.

Stop: A moulding used to hold, position, or separate window or door parts. Also, the moulding or component on the inside of a window frame against which the window sash rests or closes. Also called a bead, side stop, window stop, and parting stop.

Super window: A generic term for a window with a very low U-value. Typically it incorporates multiple glazings, low-E coatings, gas fills, and an insulating spacer.

Tempered glass: Glass heat treated to withstand greater than normal forces on its surface. When it breaks, it shatters into small pieces to reduce hazard.

Tenon: A rectangular projection cut out of a piece of wood for insertion into a mortise.

Thermal break: A thermally insulating or low-conductance material used between interior and exterior aluminum (or other conductive material) window and door components.

Tilt window: A single- or double-hung window whose operable sash can be tilted into a room to allow cleaning of the exterior surface on the inside.

Transom: Window used over the top of a door or window, primarily for additional light and aesthetic value.

Triple glazing: Use of three panes of glass or plastic with two airspaces between. Generally refers to a sealed insulating unit.

True divided lites (TDLs): Traditional window construction incorporating smaller panes of glass actually separated by muntins, rather than simulating such an appearance with larger lites of glass and a muntin grid or grille placed between or on the surfaces of the glass layers.

Two-step distributor: An industry term for a wholesale company which buys building products from the manufacturer and sells them to lumber yards and home centers, which in turn sell to builders, contractors, and homeowners. A wholesaler which buys building products from a manufacturer and sells them to builders, contractors, and homeowners is referred to as a one-step distributor.

U-factor: Rate of heat flow-value through a building component, from room air to outside air. Also referred to as U-value. The lower the U-factor, the better the insulating value. U-fact, a rating more generally used in the window industry, is the recipricol of R-value, a rating commonly used in the insulation industry.

Ultraviolet light (UV): Invisible rays of solar radiation at the short-wavelength violet end of the spectrum. Ultraviolet rays can cause fading of paint finishes, carpets, and fabrics, as well as deterioration of some materials.

Vinyl: Generic term for polyvinylchloride or PVC, an extruded material used for window and door framing.

Warm-edge: A type of insulating glass construction using an airspacer offering lower thermal conductance than traditional aluminum spacer. Warm-edge i.g. units typically offer higher resistance to condensation and an incremental improvement in window energy performance.

WDMA: Window and Door Manufacturers Association. Formerly the National Wood Window and Door Association, this trade organization has established many standards related to wood window and door products.

Weatherstripping: A material or device used to seal the openings, gaps, or cracks of venting window and door units to prevent water and air infiltration.

Weep hole: A small opening in window or sill member through which water may drain to the building exterior.

Weld: A term used for a type of corner construction, used with vinyl and other types of windows and doors, in which a small amount of material at the two pieces are melted or softened, then pushed together to form a single piece. This is also referred to commonly as a fusion-weld.

Wildland/urban interface: An area where buildings are bounded by wild or natural areas, which are a particular concern in regions where wild fires are a concern. Some fire and code officials are looking at the establishment of fire-resistance requirements for exterior building products in these "interface" areas.

Windload: Force exerted on a surface by moving air.