おりやま

おりやま【折り山】

the side(s) of a fold [crease].

●折り山をなくす[つぶす] remove [straighten out] a fold [crease]; smooth out a fold [crease]; press out a fold [crease]

・きちんとプリントの折り山をそろえてからとじなさい. Make sure the folds are properly aligned before binding the printed sheets [putting the prints in a folder].