noun
double window; double-glazed window; storm window
Refers to a window with two layers, either for insulation (double glazing) or as an additional outer window (storm window).
寒い地域では、二重窓が断熱に役立つ。
In cold regions, double-glazed windows help with insulation.
この家は二重窓になっているので、外の音がほとんど聞こえない。
This house has double windows, so you can hardly hear outside noise.
断熱窓 emphasizes thermal insulation, while 二重窓 can refer to any double window, including storm windows.
Compound of 二重 (にじゅう, 'double') and 窓 (まど, 'window').