Buoy: A metal or wooden floating object usually anchored or moored on a dangerous rock or shoal at the entrance of a harbor, or at the edge of a channel, as a guide to navigators. Mooring buoys are also used as anchorages to secure vessels in specified positions. Buoys are often named according to shape, as the can buoy, which is a metal cylinder; the nun buoy, which has the shape of a truncated cone; and the spar buoy, which is an upright post, or spar, anchored at one end. The bell buoy is surmounted by a bell that is sounded by the action of the waves; the gong buoy, similarly operated, produces several distinctive, bell-like tones; and the whistle or horn buoy is fitted with a device by which air, compressed by the action of the waves, is led to escape through a whistle. Lighted buoys are extremely important aids to navigation at night; they are battery powered and emit light signals of different color and duration.
Each nation has a buoyage system of shapes, colors, numbers, and markings to indicate dangers to navigation. In the United States buoyage system, red, even-numbered buoys mark the starboard (right-hand) side of a channel, when coming from seaward, and black odd-numbered buoys indicate the port (left-hand) side. Buoys with red and black horizontal stripes mark channel junctions and isolated dangers.