Closed lines

Closed line or closed lines could refer to:


 * Closed curve, a curve in mathematics where the two ends meet
 * Closed line segment, a line segment in mathematics that includes both its endpoints
 * Defunct airlines, or air travel companies that no longer exist
 * Line (formation), a military formation in which soldiers are packed together into rows
 * Close order formation, another military formation in which soldiers are packed together into a grid
 * Abandoned railway, or a train line that is no longer used