A long cord used to gather fabric, especially in clothing, is called a drawstring. If the wind feels unexpectedly chilly this morning, you can put up the hood of your sweatshirt and pull the drawstring tight.
You might find a drawstring in the hood of your coat, the waist of your sweatpants, or the opening in your backpack. Typically, a drawstring hangs loose unless it's tightened or tied shut. Most drawstrings are laced through loops of material, or into a tube, like the waist of a skirt. Little kids' clothes can't legally have drawstrings, since they're considered hazardous.