noun
fold line; crease line
A line marked on paper, cardboard, or other material to indicate where to fold. Common in origami, packaging, and crafts.
折り線に沿って紙を折ってください。
Please fold the paper along the fold line.
この箱の折り線がわかりにくい。
The fold lines on this box are hard to see.
折り目 refers to the actual crease or fold mark after folding, while 折り線 is the printed or drawn line indicating where to fold.
Compound of 折り (ori, 'folding') and 線 (sen, 'line').