A series of letters followed by plus and minus signs that describes the various physical parameters for a man.
Because "Bears" mean so many things to different people, because bears come in all shapes and sizes and have different sexual proclivities, because classified ad prices are SOOOOOO expensive, Bob Donohugh and Jeff Stoner (while eating lunch at a Boulder, Colorado, Wendy's on Thanksgiving weekend, 1989) came up with this incredibly-scientific system to describe bears and bear-like men.
For more details, go here: http://www.resourcesforbears.com/NBCS/