Double Hung window:  Is the most common window types. it consists of an upper and lower sash that slide vertically past each other in a solid frame.

Double glazing: Two panes of glass , separated by an air space, used to increase energy efficiency and provide other performance benefits.

Double Strength Glass:  Sheet glass with a thickness between 0.115 to 0.133 inch, 3 to 3.38mm or approximately 1/8” used in larger windows.

Dormer Window: Is window with a roof of its own, positioned, at least in part, within the slope of the roof.

Drip cap:  A molding placed on the top of the head brickmold or casing of a window frame.

Desiccant: Is a substance that absorbs water vapor. It is most commonly used in insulated glass to  remove humidity that would normally degrade or even destroy products sensitive to moisture.

Dual-action window: Else call tilt and turn. sash tilts in from the top for ventilation and swings in from the side

Dead-air space: the space between the panes of glass of an I.G. Unit