Refers to curtains or drapes hung at a window. A straightforward noun with no special usage notes.
I opened the curtains and let the morning sun into the room.
I bought new curtains and changed the atmosphere of the room.
Standard kanji spelling.
Abbreviated kanji form; less common but still encountered.
Compound of 窓 (mado, 'window') and 掛け (kake, 'hanging'), from the verb 掛ける (kakeru, 'to hang').