noun
loop line; circle line; circle route
Refers to a transit line (train, bus, etc.) that runs in a loop, often in urban areas. Common in route names like 山手線 (Yamanote Line) or 大阪環状線 (Osaka Loop Line).
東京の山手線は有名な循環線です。
Tokyo's Yamanote Line is a famous loop line.
このバスは市内を一周する循環線です
This bus is a circle route that goes around the city.