Terminology Guide
How to "Talk Windows"

Apron
Inside flat trim member which is used under the stool at the bottom of the window.

Block Frame Window
A block frame window is used when replacing the wood sash of an old double hung window.

Check Rail
On a double-hung window, the bottom rail of the upper sash and the upper rail of the lower sash, where the lock is mounted.

Curb
A watertight wall or frame used to frame under the sill or above the header in a rough opening for a window in a frame wall.

Fixed
Non-venting or non-operable.

Flush Fin Window
A replacement window with Flush Fin is used when replacing an existing aluminum sliding window. This is the commonly used replacement window type.

Gasket
A pliable, flexible continuous strip of material used to affect a watertight seal between sash and frame of roof windows much like a seal around a refrigerator door.

Glass Pane
In the window (shown) there are two panes of glass, one in the top sash and one in the bottom sash.

Glazing
The glass panes or lights in the sash of a window. Also the act of installing lights of glass in a window sash.

Head
The main horizontal member forming the top of the window or door frame.

Head Jamb
Groove at top of the window which allows the window sashes to slide into place and seat inside the window frame.

Hinged Models
Awning: Hinged at the top and opens out from the bottom.
Casement: Hinged on one side and swings open like a door.
Hopper: Hinged at the bottom and opens in or out from the top

Hopper Window Units
A Hopper Window Unit is a window unit that is hinged at the bottom and opens inward from the top. The Hopper Window Unit features a brass plated locking mechanism at the top and brass plated chains on the rails making this a functioning window unit.

Insulated Glass
Glazing manufactured with insulated air space(s) between two (double-pane) or three (triple-pane) layers of glass.

Lite
A piece of glass surrounded by wood, a pane. Often used when referring to multiple panes (a window, a pane of glass within a window).

Lower Sash
The bottom portion of the window comprised of a pane of glass set inside a frame. It's fixed on a single hung window and slides up and down in a double hung window.

Molding
An ornamental exterior trim around the perimeter of a frame.

Mortise
A slot or rectangular cavity cut into a piece of wood to receive another part.

Mullion
A vertical space separating two architectural unit's such as a stud pocket between an entry door and a side lite. Not the divider bars between the window panes.

Muntin
The shorter pane divider components that do not go all the way across the opening in one piece but rather go only between the bars, rails or frame in short segments.

Operator
A metal arm and gear which allows for easy operation or closing of projecting windows.

Pane
As in window pane, also called a lite. A sheet of glass for glazing a window. After installation, the pane is referred to as a "lite" or "window lite."

Rails
A horizontal component separating glass panes that goes between a pair of stiles just like the top, bottom and/or intermediate rails on a door. To be a rail, the part must cross the entire width of the opening on one unbroken piece.

Rough Opening
The frame opening where a window, door or skylight unit will be installed.

Side Jamb
Grooves in window that allows the window sashes to slide up and down or side to side (Side Jamb joins the sill which forms the bottom of the window frame).

Sill
Located at the very bottom of the window, the sill is usually sloped to allow water to run off the bottom of the window in rain or during cleaning. Horizontal member that forms the bottom of a window frame.

Simulated Divided Lite
A method of constructing windows in which muntins are affixed to the inside and outside of a panel of insulated glass to simulate the look of true divided lite.

Single Hung Window Units
In a Single Hung Window, the top sash is fixed and doesn't move whereas the bottom sash is operable.

Sliding Models
There are five types of sliding windows:

Cottage Double-Hung: A double-hung window in which the upper sash is shorter than the lower sash.

Tilt and Turn Windows: Swing from the side or pivot from the middle. Others pivot from both bottom (like a hopper) and the side (like a casement). Also called Dual Action.

Double-Hung Windows: Include offset upper and lower sashes, which can both move up and down in the frame. A window having two vertically sliding sash, each closing a different part of the window. the weight of each sash is counterbalanced for ease of opening and closing. Also called Double-Hung Sash.

Horizontal Sliders: Consist of two sashes, one or both of which slide horizontally in the frame.

Single-Hung Windows: Include one fixed sash (usually at the top one) and one that moves up and down in the frame.

Sloped Sill Adapter
A sloped sill adapter is used to cover the gap between the old sloped sill window and the new block frame window. It adapts a new window to the existing sloping sill.

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

Stop
A wood trim member nailed to the window frame to hold, position or separate window parts. The stop is often molded into the jamb liners on sliding windows.

Tempered Glass
Glass that has been heat-treated to improve glass strength. Tempered glass is sometimes called safety glass because when it breaks, it creates pebble-sized particles rather than sharp shards and slivers.

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

Transom
A smaller window above a door or another window. A transom joint is also the horizontal joining area between two window units which are stacked one on top of the other.

Trim or Casing
The trim extends beyond the end of the window frame on the outside of the window. This allows fitting flush with the exterior wall when the window is installed.

True Divided Lite
A term that refers to windows in which multiple individual panes of glass or lites are assembled in the sash using muntins.

Upper Sash
The top portion of the window comprised of a pane of glass set inside a frame. It is fixed in a single hung window and slides up and down in a double hung window.