Efficiency in basketball is measured in a multitude of ways, so it can be confusing trying to keep it all straight. The NBA tracks individual efficiency in four ways: efficiency (EFF), player efficiency rating (PER), offensive efficiency rating (OER), and defensive efficiency rating (DER). The Euroleague tracks efficiency through the performance index rating (PIR) instead of efficiency.
EFF is measured by adding up all of the production stats (points, rebounds, assists, steals, and blocks), subtracting all missed shots (field goals and free throws) and turnovers, then dividing by games played. PER includes fouls drawn as a positive and fouls committed and shots rejected as negatives.