Box plus-minus is based on box score for evaluating basketball players’ quality and contribution to the team from play-by-play regression.
BPM takes box score stats from an individual and team level and tries to estimate player performance relative to the NBA average. Since BPM is a per-100-possession stat where 0.0 is league average, +5 means the player is 5 points better than an average player over 100 possessions (which is about All-NBA level), -2 is replacement level, and -5 is really bad.
Box plus-minus is invented by Daniel Myers.