contre-fenêtre

Etymology
From. From being a window counter/opposite to the primary door, the anti-facing window.

Noun

 * 1) a secondary window placed inside or outside of the primary window
 * 2) a storm window an exterior window placed outside the primary window to improve weatherproofing

Coordinate terms

 * screen window
 * / /  aluminum window / aluminium window
 * / /  vinyl window
 * / /  PVC window
 * / /  PVC window