限界线

限界线	xiàn jiè xiàn	boundary / dividing line
限	xiàn	to limit / to restrict / (bound form) limit / bound
界	jiè	(bound form) boundary; border / (bound form) realm
界线	jiè xiàn	limits / bounds / dividing line
线	xiàn	variant of 线
线	xiàn	thread / string / wire / line / CL:条,股,根 / (after a number) tier (unofficial ranking of a Chinese city)