Windows & Doors Glossary

Windows & doors, word by word

Windows & doors come with their own vocabulary, from U-factor and low-E to astragals and sidelites, and this guide translates all 164 terms into plain English.

When you shop for replacement windows or a new entry door, the brochures, quotes and energy labels assume you already speak the language. Knowing the words helps you compare products fairly, ask sharper questions and choose upgrades that actually lower your energy bills.

Thrush & Son® has installed windows & doors on Miami Valley homes since 1960. Switch between the window and door glossaries below, or start with the energy label every new window carries.

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Window Terminology visual featuring professional window installation highlighting key components, energy efficiency, and precision craftsmanship.
Read the Label

Windows & doors energy labels, decoded

Rated windows & doors carry a performance label. Here’s what each number means and which way you want it to go.

  • U-FactorHow fast heat escapes. Lower is better, and ENERGY STAR sets the maximum for each climate zone.
  • Solar Heat Gain CoefficientHow much of the sun’s heat comes through. Lower keeps summer rooms cooler.
  • Visible TransmittanceHow much daylight gets in. Higher means brighter rooms.
  • Air LeakageHow much air sneaks through. Lower means fewer drafts.
  • Condensation ResistanceHow well the window resists interior condensation, on a 1–100 scale. Higher is better.
Windows & Doors Terminology: Insulated Glass Unit cross-section showing triple-pane window layers and spacers set against blue architectural blueprints, illustrating modern energy-efficient window design
The Glossary

164 windows & doors terms

Flip between windows & doors, then jump to a category. Terms are grouped by where you’ll find them, not just A to Z.

Windows & doors · window termsWindow styles & configurations

How a window opens decides where it fits best. These are the windows & doors styles you’ll see in any showroom.

Awning Window
Hinged at the top and opens outward from the bottom, so it can stay open in light rain.
Bay Window
Three windows set at angles that project out from the wall, usually a large center unit with two narrower flankers.
Bow Window
Four or more equal windows joined in a gentle curve that projects out from the house.
Casement Windows
Hinged on the side and cranked open outward, sealing tightly against the frame when closed.
Double Hung Window
Two sashes that both slide up and down, and usually tilt in for easy cleaning.
Single Hung Window
Looks like a double hung, but only the bottom sash moves; the top sash is fixed.
Sliding Window
One or more sashes that glide sideways along a track.
Three Lite Slider
A sliding window with three sections, typically a fixed center and two operating ends.
Fixed Unit Window
A window that doesn’t open, built to bring in light and views.
Picture Window
A large fixed window designed to frame an outdoor view with as little frame as possible.
Hopper Window
Hinged at the bottom and tilts inward from the top, common in basements.
Garden Window
A small box-shaped window that projects outward, with glass on the top and sides for plants.
Storm Window
A secondary window installed over an existing one for extra protection and insulation.
Factory Mulled
Two or more windows joined together at the factory into one unit, rather than on site.
Vinyl Clad Window
A window with a wood interior and a protective vinyl exterior skin.
Witch Window or Coffin Window
A window set at a slant in a gable wall, following the roofline; a New England tradition.

Windows & doors · window termsGlass, energy & performance

Most of the energy story in windows & doors happens in the glass. These terms explain what’s between the panes.

Glazing
The glass in a window or door, or the act of installing it.
Single Pane Glass
One layer of glass with no insulating space; common in older homes and poor at stopping heat loss.
Double Pane Glass
Two panes of glass separated by a sealed space, often filled with gas, for better insulation.
Triple Pane Glass
Three panes and two insulating spaces for the highest comfort and noise reduction.
Insulated Glass
Two or more panes sealed together with a spacer around the edge, also called an insulated glass unit (IGU).
Window Pane
A single sheet of glass in a window.
Argon Gas
A clear, harmless gas sealed between panes; it slows heat transfer better than air.
Krypton Gas
A denser insulating gas than argon, often used in triple-pane glass with narrow spaces.
Low – E Coating
A microscopically thin metal coating on the glass that reflects heat while letting light through.
Laminated Glass
Two layers of glass bonded to a plastic interlayer, so it holds together if broken.
Tempered Glass
Glass heat-treated to be about four times stronger than standard glass; it breaks into small, dull pieces.
Obscure Glass
Textured or frosted glass that lets light in while blocking a clear view, common in bathrooms.
Grid
Decorative bars that give the look of divided panes; often placed between the glass.
Muntins
Strips that divide a window into smaller panes, either true divided lites or decorative grids.
Spacers / Spacer Systems
The strip that separates the panes in insulated glass and seals the edge.
Warm Edge Spacer
A spacer made to conduct less heat than plain aluminum, which reduces edge condensation.
Super Spacer
A flexible, non-metal foam spacer brand used for warm-edge insulated glass.
Intercept Spacer
A one-piece, U-shaped warm-edge spacer system brand that seals the edge of insulated glass.
U-Value
How fast a window loses heat. Lower numbers mean better insulation; also called U-factor.
R-Value
Resistance to heat flow. Higher numbers insulate better.
Solar Heat Gain (SHG)
How much of the sun’s heat passes through the glass. Lower numbers keep summer heat out.
Thermal Conductivity
How easily a material carries heat. Glass and metal conduct more than vinyl or gas.
Thermal Expansion
How much a material grows and shrinks with temperature, which affects seals and fit.
Condensation
Moisture that forms on glass when warm, humid air hits a cold surface.
Condensation Factor
A rating of how well a window resists interior condensation. Higher is better.
Infiltration
Outside air leaking in around the sash or frame.

Windows & doors · window termsFrame & sash parts

The frame and sash hold everything together. Strong, well-sealed frames are what make windows & doors last.

Window Frame
The fixed outer structure that holds the sash and attaches to the wall.
Sash
The frame that holds the glass, whether it moves or is fixed.
Rail
A horizontal piece of the sash at the top or bottom.
Stiles
The vertical side pieces of a sash.
Jamb
The vertical sides and top of the window frame.
Jamb Cover
Trim that covers an existing jamb, often during a replacement.
Jamb Extension
An added strip that brings the frame flush with a thicker interior wall.
Jamb Liner
The track inside the side jamb that the sashes slide in on a hung window.
Balance
The spring or counterweight system that holds a hung sash in place when you raise it.
Parting Stop
A thin strip in the jamb that separates the upper and lower sashes.
Brickmold
Exterior trim around the window that covers the gap between the frame and the wall.
Casing
Trim around the window on the inside or outside wall.
Window Stool
The interior ledge at the bottom of the window, often called the sill.
Window Apron
The trim board below the stool on the interior wall.
Glazing Beads
Strips that hold the glass in place inside the sash.
Glazing Gasket
A rubber or vinyl seal between the glass and the sash.
Weather Stripping
Flexible seals where the sash meets the frame that block drafts and water.
Weep Holes
Small openings at the bottom of the frame that let water drain out.
Nail Fin
A flange around a new-construction window frame that is nailed to the wall sheathing.
PVC
Polyvinyl chloride, the rigid plastic used to make vinyl window frames.
Cap Stock
A tough outer layer bonded over the vinyl frame for color and weather resistance.
Fusion Weld
Joining vinyl frame corners with heat so they become one solid, airtight piece.
Sash Reinforcement
Metal or composite inserts that stiffen the sash, especially on large windows.
Innergy Rigid Thermal Reinforcements
A brand of composite frame reinforcement that adds strength without metal’s heat loss.

Windows & doors · window termsHardware & installation

Even the best windows & doors leak if they’re installed poorly. These are the hardware and installation words on your quote.

Hardware
The working parts of a window, such as locks, cranks, hinges and latches.
Sash Lock
The lock that secures a hung window and pulls the sashes together.
Cam Lock
A rotating lock that pulls the sashes tight as it turns.
Keeper
The part of a lock that the latch hooks into.
Tilt Latch
The button or slide on top of a hung sash that releases it to tilt in for cleaning.
Rough Opening
The framed hole in the wall that the window fits into.
United Inch
Width plus height in inches, a common way to size and price windows.
Shim
A thin wedge used to level and square the window in the opening.
Fasteners
Screws and nails that anchor the window in the opening.
Nailing
Securing the window through the nail fin or frame as the manufacturer specifies.
Flashing
Waterproof material around the opening that directs water away from the wall.
Window Wrap
Flexible waterproof tape or membrane that seals the rough opening.
Insulation
Material packed between the frame and the opening to stop drafts.
Cellulose Insulation
Insulation made mostly from recycled paper, often blown into walls and attics.
Caulk
A flexible sealant used around the frame to keep air and water out.
Caulking
The act of applying caulk to seal a joint.
Sill Failure
Rot or breakdown of the sill below a window, usually from long-term water exposure.
Chalking
A powdery film that forms on aging painted or vinyl surfaces.

Windows & doors · window termsStandards, codes & ratings

These groups test and rate windows & doors, so the numbers on a label mean the same thing from brand to brand.

NFRC
The National Fenestration Rating Council, which tests and labels window energy performance.
AAMA
The American Architectural Manufacturers Association, which sets performance standards for windows and doors.
WDMA
The Window & Door Manufacturers Association, a trade group that publishes product standards.
Egress
A window large enough to escape through in an emergency; building codes require one in bedrooms.
Material Safety Data Sheets (MSDS)
Manufacturer documents listing a product’s hazards and safe handling; now called SDS.

Windows & doors · door termsThe door frame

The frame is what anchors windows & doors to the house. These are its parts, from the head jamb to the threshold.

Brick Molding / Trim / Architrave
The exterior trim around the door frame that covers the gap to the wall.
Casing / Trim
The trim around the door on the inside wall.
Door Stop
The strip on the jamb that the door closes against.
Head Jamb
The top piece of the door frame.
Jamb
The vertical sides of the door frame.
Mullion
A vertical post that joins a door to a sidelite or another door.
Sill / Threshold
The bottom of the door frame that sheds water and seals against the door.

Windows & doors · door termsParts of the door slab

A door slab is built like furniture. These windows & doors terms name every piece of it.

Astragal
A vertical strip on one door of a pair that covers and seals the gap between them.
Bore Hole
The hole drilled through the door for the knob or lever.
Bottom Rail
The horizontal piece at the bottom of the door.
Center Stile
A vertical piece in the middle of a panel door.
Core
The inside of the door, such as foam, wood or composite, which affects strength and insulation.
Dentil Shelf
A decorative ledge with small, tooth-like blocks, often above the lower panel.
Door Shoe / Door Sweep
A strip at the bottom of the door that seals against the threshold.
Frieze Rail / Intermediate Rail / Cross Rail
A horizontal piece between the top and lock rails.
Hinge Stile
The vertical edge of the door where the hinges attach.
Lock Rail / Middle Rail
The horizontal piece at lock height.
Lock Stile
The vertical edge of the door where the lock goes.
Panel
A flat or raised section set between the stiles and rails.
Rail
Any horizontal piece of the door.
Stiles
The vertical pieces of the door.
Sticking
The shaped edge profile around the panels.
Top Rail
The horizontal piece at the top of the door.

Windows & doors · door termsDoor hardware

Hardware is where you touch windows & doors every day, and where security and weather sealing happen.

Hinge
The pivot that connects the door to the frame.
Ball Bearing Hinge
A hinge with bearings for smoother swing on heavy doors.
Radius Hinge
A hinge with rounded corners to fit a rounded recess.
Square Hinge
A hinge with square corners to fit a square recess.
Strap Hinges
Long, decorative surface hinges often used on rustic or carriage-style doors.
Lockset / Hardware
The full package of handle, latch and lock.
Cylindrical Lock
A common lock that fits in a round bore hole through the door.
Mortise Lock
A heavy-duty lock set into a deep pocket in the door edge.
Multi-Point Locking System
A lock that secures the door at several points along the edge with one turn.
Lever Handle
A handle you push down rather than turn; easier for many hands.
Knob Closure
A round knob used to open and latch the door.
Thumb Latch
A traditional latch operated by pressing a lever with your thumb.
Flush Bolt
A bolt set into the edge of the inactive door of a pair to lock it in place.
Strike Plate
The metal plate on the jamb where the latch or bolt catches.
Clavos
Decorative nail heads used on rustic or Spanish-style doors.
Sill Pan
A waterproof tray under the threshold that catches water and drains it out.
Weather Strip
Seals around the door that block drafts and water.

Windows & doors · door termsDoor types

Material and style decide how a door looks, insulates and holds up. Here are the windows & doors types we install most.

Active Door
The door in a pair that you open first and that holds the lock.
Passive Door
The door in a pair that stays fixed until released.
Direct Set
Glass set directly into the frame with no operating sash.
Double Acting Door
A door that swings both ways.
Dutch Door
A door split horizontally so the top and bottom open separately.
Fiberglass Door
A durable, low-maintenance door that resists dents and can look like wood.
Steel Door
A strong, secure, cost-effective door with an insulated core.
Flush Door
A door with a smooth, flat face and no panels.
French Door
A door with glass lites running most of its height, often in pairs.
Ledge Door / Batten Door
A door made of vertical boards held together with horizontal braces.
Paneled Door
A door built with stiles, rails and inset panels.

Windows & doors · door termsGlass, finishes & installation

The finishing words: glass, trim, installation and the shop terms you may hear when ordering windows & doors.

Door Lite(s) / Glazing
The glass in a door.
Came, Caming
The metal strips that hold pieces of decorative glass together.
Muntin / Uprite
A bar that divides door glass into smaller sections.
Sidelite
A tall, narrow window beside the door.
Operable Sidelite / Vented Sidelite
A sidelite that opens for fresh air.
Transom
A window or opening above the door.
Transom Lite
The glass panel in a transom.
Tempered Glass / Safety Glass
Strengthened glass required in doors that breaks into small, dull pieces.
Sash In Frame
A glass insert built in its own frame and set into the door.
Mull Post
The post where a door and sidelite are joined.
Door Slab
The door alone, without the frame or hardware.
Door Unit
The complete door with frame, hinges and threshold.
Pre – Hung
A door already hung in its frame at the factory, ready to install.
Rough Opening
The framed hole in the wall that the door unit fits into.
Shim
A thin wedge used to plumb and square the door in the opening.
Backset
The distance from the door edge to the center of the bore hole.
Rabbet
A recessed step cut into the frame that the door closes against.
Mortise & Tenon Joinery
A strong joint where a tongue on one piece fits into a slot in another.
Ogee
An S-shaped decorative molding profile.
Shaker / Square
A clean style with flat panels and square edges.
Distressing Wood
Hand-aging wood for a weathered, rustic look.
Prefinished
Stained or painted at the factory before installation.
Primed
Coated with primer and ready for paint.
Trim
The finish moldings around the door.
Why It Matters

Why understanding windows & doors terminology matters

Two windows can look identical in a showroom and perform very differently on a January night in Ohio. The difference is written in the window terminology: the glass package, the spacer, the gas fill, the frame reinforcement and the installation details. When you understand those words, you can compare windows & doors on what matters instead of on price alone.

The same is true across windows & doors of every kind, and especially for entry doors. A fiberglass slab with a foam core and a multi-point lock is a very different product from a hollow steel door with a single latch, even if both are painted the same color. Read the U.S. Department of Energy guide to energy-efficient windows for more on ratings, then see what we install on our windows & doors page.

Want more plain-English guides to windows & doors? Find them on The Home Improvement Minute.

Comparing windows & doors quotes?Bring them to us. We’ll explain every term on the page and give you a written estimate of our own, with no pressure.

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