1.
section; segment; interval (of a route or range)
A defined portion of a route, track, or range, often used for transportation routes, distance measurements, or mathematical intervals.
Common collocations: 区間運転 (service on a limited section of a train line), 区間快速 (semi-rapid train that runs express on a limited section). In mathematics, 区間 refers to an interval on a number line. Often appears on train signs and announcements to indicate which portion of a route is affected by delays or service changes. Related: 区域 (area, zone — refers to a two-dimensional area rather than a linear section).