A ribbon or cord that's inserted through a casing. You pull and tie the drawstring to tighten or close an edge.

a tie consisting of a cord that goes through a seam around an opening; "he pulled the drawstring and closed the bag"

a soft bag with a gathered drawstring closure. The drawstring, once synched, may form into purse straps or have a separate strap.

A cord laced through a hem or casing, usually added to a waistline, cuff or hood that tightens or loosens the opening when pulled or released. Originally a feature only of active wear, drawstrings are now commonly used in all types of sportswear.