The Knotted Loop is probably the most useful item to a kiter. It can be used on any kite as a place to secure the flying line. We use it on everything from the smallest to the biggest kites. It is found on all the 'state-of-the-art' stunt kites.
It is merely a length of line, usually about a foot, with the ends tied in either a Figure Eight or an Overhand Knot. I prefer the Figure Eight because it is both stronger and bulkier, a more reliable 'stop' knot than the Overhand. An Overhand Knot is only a 50% knot.