noun
crease (writing guide); creasing; crease line
Refers to a pre-made crease or fold line on paper, often used as a guide for writing or folding. Common in stationery and paper-craft contexts.
この便箋には折罫が入っているので、まっすぐに折れます。
This writing paper has a crease line, so you can fold it straight.
折罫に沿って手紙を三つ折りにしてください。
Please fold the letter in thirds along the crease lines.
罫線 refers to ruled lines in general (e.g., on notebook paper), while 折罫 specifically means a crease or fold line used as a guide.
Compound of 折り (ori, 'folding') and 罫 (kei, 'ruled line'). The kanji 罫 is associated with lines or rules, and the combination describes a line made by folding or a crease used as a guide.