What is Buoy?

Legal Definition
A buoy (/ˈbɔɪ/, also /ˈbwɔɪ/ or US /ˈb/) is a floating device that can have many purposes. It can be anchored (stationary) or allowed to drift with the sea wave. The word, of Old French or Middle Dutch origin, is (in British English) now most commonly pronounced /ˈbɔɪ/ (identical with boy, as in buoyant). In American English the pronunciation is closer to "boo-ee."
-- Wikipedia
Legal Definition
A piece of wood, or an empty barrel, floating on the water, to show the place where it is shallow, to indicate the danger there is to navigation. The act of Congress, approved the 28th September, 1850, enacts, " that all buoys along the coast, in bays, harbors, sounds, or channels, shall be colored and numbered, so that passing up the coast or sound, or entering the bay, harbor or channel, red buoys with even numbers, shall be passed on the starboard hand, black buoys, with uneven numbers, on the port hand, and buoys with red and black stripes on either hand. Buoys in channel ways to be colored with alternate white and black perpendicular stripes."
-- Bouviers Law Dictionary
Legal Definition
In maritime law. A piece of wood or cork or a barrel, raft or other thing, made secure and floating upon a stream or bay, intended as a guide and warning to mariners, by marking a spot where the water is shallow or where there is a reef or other danger to navigation or to mark the ceurse of a devious channel.
-- Black's Law Dictionary