Usually a red plastic ball of at least 24 inches in diameter, with a large ring attached. Hook the ring on the anchor rope and heave the buoy overboard. Drive the boat upwind or upcurrent. Presto! The anchor is pulled up quickly to the buoy using horsepower instead of human power.
Any material sunk offshore for the express purpose of attracting fish. Old boats, concrete culverts, metal pipe, the list is endless. Most states now require a permit before dumping because non-practical material was being used, objects that rusted quickly, polluted or were a hazard to shrimpnets.