noun
territorial water boundary line; territorial limits
Refers to the line demarcating a nation's territorial waters, often used in legal, maritime, or geopolitical contexts.
その島は領海線のすぐ内側にある。
The island is just inside the territorial water boundary line.
領海線を越えた外国船は警告を受
The foreign vessel that crossed the territorial limits was warned.
国境線 is a land border line, whereas 領海線 is a maritime boundary line.
Compound of 領海 (territorial waters) + 線 (line). The term is straightforward and modern, with no obscure historical derivation.