Surface-following discus buoy
A buoy of which the body is a shallow disk, usually surmounted by a pillar or tower superstructure. The buoy has a large cross-section at the water-level, so that it follows the surface of the sea under the influences of swell and waves.
Please note that this is the term as it stands in the original IALA Dictionary edition (1970-1989)
International Association of Marine Aids to Navigation and Lighthouse Authorities - AISM