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

Awning window: A window that has a single sash in which the bottom of the sash swings out.

Astragal: The center member of a double door, which is attached to the inactive door panel.

Bay window: Three or more windows in a row, usually made up of a large unit in the center and one unit on either side at 30°, 45° or 90° angles to the wall.

Bow window: Four or more window units together in a bow formation.

Brick mould: Outside moulding around the window frame to cover jambs.

Casing: Inside casing is a flat, decorative moulding that covers the inside edge of the jambs and the rough openings between the window unit and the wall.

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.

Dormer: A space, which protrudes from the roof, usually including one or more windows.

Double-glazing:  Use of two panes of glass in a window to increase energy efficiency and provide other performance benefits.

Double-hung:  A window with two vertical operating sashes that slide up and down.

Double rafter:  The doubling (side by side) of the roof members to reinforce an opening in the roof for a slope-glazing installation.

Drip cap:  A moulding placed on the top of the head brick mould or casing of a window frame.

Fenestration: An architectural term referring to the placement of windows in a wall.

Finger-jointing:  A way of joining pieces of wood together to form longer lengths.

Fixed:  Non-venting or doesn’t open.

Flashing:  A metal or plastic strip attached to the outside of the head or side jambs to provide a weather barrier. It prevents leakage between the frame and the wall.

Gasket: A strip of material used to create a watertight seal between the sash and the frame of a window.

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

Glazing bead:  A plastic or wood strip applied to the window sash around the glass.

Glazing stop:  The part of the sash or door panel which holds the glass in place.

Grill:  A bar used to visually separate glass into multiple lights. Also called a window pane divider or a muntin.

Head: The main horizontal member forming the top of the window or doorframe.

Head board:  A flat board that fits the contour of a bow or bay window at the top and that finishes off the ceiling inside the window.

Header:  A heavy beam extended across the top of the rough opening to help support the weight of the building.

Jamb liner:  Metal or plastic covering the inside surface and head jambs of sliding windows.

Keeper: The part of a casement window lock that looks like a hook.

Lift: Handle or grip installed on the bottom rail of the lower sash of a double-hung window to make it easier to raise or lower the sash.

Light:  (also spelled lite) Glazing framed by muntins and/or sash in a window or door.

Low-E glass:  A common term used to refer to glass, which has low emissivity due to a metal coating on the glass surface between the two lights of glass to restrict the passage of radiant heat.

Masonry openings: The opening in a masonry wall to accept a window or door unit.

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

Mortise:  A slit cut into a piece of wood to receive another part.

Mullion:  The joints between single windows in a multiple window unit.

Mullion casing:  An interior or exterior casing to cover the mullion joint between single windows.

Muntin:  A bar used to visually separate glass into multiple lights. Also called a window pane divider or a grill.

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

Outer frame member:  The exterior protruding portion of a window frame, which has no exterior casing.

Panel:  Usually refers to the separate panel or panels in a doorframe.

Picture frame casing:  The use of casing on all four sides of the interior of a window, replacing the stool and apron at the sill.

Pitch:  The degree of the slope of a roof.

Rafter: Structural members of a roof that support the roof load.

Rails:  The horizontal members of a window sash or door panel.

Rough opening:  The opening left in a frame wall to receive a window or door unit.

Rough sill:  The horizontal rough framing area which forms the bottom of the rough opening.

Sash balance: A system of weights, cords and/or coiled springs which assist in raising double-hung sash and tend to keep the sash in any placed position by counterbalancing the weight of the sash.

Sash cord:  In double-hung windows, the rope or chain that attaches the sash to the counter balance.

Sash lock:  A lock applied to the checkrails of a sliding window or at the open edges of a projecting window to pull the checkrails tightly together or to seal the sash tightly to the frame, both for security and weather tightness.

Seat board:  A board that fits the contour of a bow or bay window at the bottom and that provides a seat or shelf space.

Shims:  Wooden wedges that are used to secure windows in the rough opening. Helps make the window level within the rough opening.

Side lights:  Tall, narrow, fixed or operating sash on either or both sides of a door to light an entryway or vestibule.

Sill:  Horizontal member that forms the bottom of a window frame.

Sill course: The row of bricks across the bottom of a rough opening.

Simulated divided light:  A method of constructing windows in which grills are attached to the inside and outside of a panel of glass to simulate the look of true divided light.

Single glazing:  Use of single panes of glass in a window.

Single-hung:  A double-hung type of window in which the top sash is fixed or inoperable.

Solar gain:  The readings of how much heat is collected inside a home through the glass of windows and doors.

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

Stool:  Inside horizontal trim member of a window sash or door panel.

Stop:  A wood trim member nailed to the window frame to secure window parts in place.

Stud:   Wood framing members, used vertically, to build a frame wall. In construction, these are eight-foot-long 2" x 4"s.

Transom:  A smaller window above a door or another window.

Triple glazing:  A sash glazed with three lights of glass, enclosing two separate air spaces.

U-Factor: A measure of heat transmission through a wall or window. The lower the U-Factor, the better the insulating value.

Vapor barrier: A watertight material used to prevent the passage of moisture into or through floors, walls and ceilings.

Venting unit:  A window or door unit that opens or operates.

Windload: Force exerted on a surface by moving air.

Window pane Divider:  A short bar used to separate glass in a sash into multiple lights. Also called a muntin or a grill.