ESPN's NBA Basketball Power Index (BPI) is a measure of team strength developed by the ESPN Analytics team. BPI is meant to be the best predictor of a team's performance for the rest of the season. BPI represents how many points above or below average a team is. BPI accounts for game-by-game efficiency, strength of schedule, pace, days of rest, game location and preseason expectations.
For more background, see: What is ESPN's NBA Basketball Power Index?