BP is the Balance Point. It's the point where the frame balances itself to the handle. If that's unclear then just put the shaft of the racket on your index finger, move forward or backward until the racket balances itself. The higher the BP the more head heavy the racket is. I'm not sure on the number, but usually anything above 300mm is head heavy, I think it's 280-300 is an even balance racket. Again, I'm not sure on that number. So 321mm BP with no string is really head heavy, considering most VT80 BP is aroun 305-315mm.