noun
thick line; heavy line; underline; border
Refers to a line that is drawn thicker than normal, often for emphasis, underlining, or as a border in documents, diagrams, or design.
重要な語句には太線を引いてください。
Please underline important words with a thick line.
表の外枠は太線で囲まれている。
The outer border of the table is drawn with a thick line.