dividing line; demarcation line
Refers to a line that separates or divides, often used in political, geographical, or conceptual contexts.
その川が二つの国の分断線になっている。
The river serves as the dividing line between the two countries.
議論の中で、意見の分断線がはっきりした。
In the discussion, the line of division in opinions became clear.
Compound of 分断 (division, splitting) and 線 (line). The exact historical derivation is uncertain, but the meaning is transparent from its components.