This is the 3170th most frequent Korean word.
경계
"Boundary," "border," or "caution/vigilance," depending on context.
Here, '경계' (boundary) refers to dividing or distinguishing areas or relationships.
그들은 새로운 이웃과 경계를 두었다.
They established boundaries with their new neighbors.
In this instance, '경계' refers to the tangible boundary or limit of an area.
그 경계의 끝까지 걸어갔다.
He walked to the end of the boundary.
Here, '경계' implies vigilance or the state of being alert to potential danger.