drawstring

/D R AO1 S T R IH0 NG/
noun
  1. 1

    A string or cord, encased in a fabric tube, with one or more small openings into the tube, on a bag or garment, allowing the item to be closed (as with a bag) or tightened (as with sweatpants or a bathing suit).

Source: https://en.wiktionary.org/wiki/drawstring