noun
line of demarcation; boundary line
A formal term for a dividing line between areas, categories, or concepts. Often used in technical, political, or abstract contexts.
両国の間に分界線が引かれた。
A line of demarcation was drawn between the two countries.
この川が県の分界線になっている。
This river serves as the boundary line between the prefectures.
Compound of 分 (ぶん, 'divide') + 界 (かい, 'boundary') + 線 (せん, 'line'). The exact historical derivation is uncertain, but the components clearly indicate a dividing line.