Argon -- A gas injected between layers of glass to increase insulation. (Argon insulates better than air.)
Dual-glazed -- A window with two panes of glass, with air or argon gas in between the layers for insulation.
Jamb -- Each side of a window's frame.
Low-E (low-emissivity) -- A coating applied to glass to reflect heat and harmful UV rays.
Muntin -- A strip used to separate glass into multiple lights. (Vertical strips between panes are known as mullions.)
Pane -- The term for the glass part or parts of a window.
R-value -- A window's resistance to heat loss or gain. The higher the value, the better.
Sash -- The framework of the window that holds the glass.
Sill -- The bottom of the window frame.
Trim -- Any decorative, nonessential parts of a window.
Triple-glazed -- A window with three panes of glass, with air or argon gas in between the layers for insulation.
U-value -- The amount of heat escaping through a window. The lower the value, the better.