区间 (qūjiān) is a noun for a defined section or segment, most commonly used for a stretch of a route (e.g., a subway line) or an interval in mathematics. It emphasizes a bounded, continuous span, unlike 空隙 (kòngxì) which focuses on a gap or crack, or 间隔 (jiàngé) which stresses the space between two points. 期间 (qījiān) is strictly temporal, while 区间 can be spatial or mathematical.