Bifurcation Mark (or Buoy)
A mark (or buoy) which, when viewed from a vessel approaching from the open sea or in the same direction as the main stream of flood tide, or in the direction established by the appropriate authority, indicates the place at which a channel divides into two.
The relative importance of the two channels is usually indicated by the use of a mark (or buoy) having a definite character (shape, colour, light character, shape of topmark, etc.).
Please note that this is the term as it stands in the original IALA Dictionary edition (1970-1989)