pleat peak; fold peak
Refers to the raised ridge formed at the top of a pleat or fold, especially in sewing, origami, or fabric work.
スカートの折り山にアイロンをかける。
I iron the pleat peaks of the skirt.
折り山がきれいに決まると
When the fold peaks are crisp, the piece looks sharp.
Compound of 折り (fold) and 山 (mountain), literally 'fold mountain', describing the raised peak of a pleat or fold.