noun
paper scoring; creasing
Refers to pressing a line into paper or cardstock to make folding easier and cleaner. Common in papercraft, bookbinding, and card making.
厚紙を折る前に筋押しをすると、きれいに仕上がります。
If you score the thick paper before folding, it will come out neatly.
このカードは筋押しが入っているので、簡単に折れます。
This card has scoring, so it folds easily.
折り筋 refers to the crease or fold line itself, while 筋押し is the action or process of making that line.
Compound of 筋 (line, groove) and 押し (pressing), from 押す (to press). The term directly describes the action of pressing a line into paper.