A reinforcing rope along the luff or the foot of the sail, it is slid into a slot along the edge of a spar (mast, boom). Found on http://www.encyclo.co.uk/local/20645
Rope sewn along one or more edges of a sail to strengthen it and take some of the stress of the cloth when it is stretched tightly. Found on http://www.glen-l.com/resources/glossary.html