noun
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、作品が引き締まる。
When the fold peaks are crisp, the piece looks sharp.