a chain or range of rocks lying at or near the surface of the water. see coral reefs, under coral.-a large vein of auriferous quartz; -- so called in australia. hence, any body of rock yielding valuable ore.-that part of a sail which is taken in or let out by means of the reef points, in order to adapt the size of the sail to the force of the wind.-to reduce the extent of (as a sail) by roiling or folding a certain portion of it and making it fast to the yard or spar.