BPM stands for Box-Score Plus Minus. It's a very complicated calculation, but the end result is supposed to tell you roughly how many points above replacement a player is worth. In this case, it says that the team is 12 points per 100 possessions better with Griffin on the floor than an average SF. To put it in perspective, in the NBA, Giannis Antetokounmpo is currently putting up one of the greatest regular seasons of all-time and he has a BPM of 11.5. Long story short, Griffin was insanely good this past season, though it was in a relatively small sample size since each college season isn't very long to begin with and he was a bench player so that shrinks the sample size even more.