From google:
“ OPS+ takes a player's on-base plus slugging percentage and normalizes the number across the entire league. It accounts for external factors like ballparks. It then adjusts so a score of 100 is league average, and 150 is 50 percent better than the league average.”
https://www.google.com/search?q=ops%2B&rlz=1CDGOYI_enUS1049US1049&oq=ops%2B&gs_lcrp=EgZjaHJvbWUyDAgAEEUYORixAxiABDIMCAEQABgUGIcCGIAEMgcIAhAAGIAEMgcIAxAAGIAEMgcIBBAAGIAEMgcIBRAAGIAEMgcIBhAAGIAEMgcIBxAAGIAEMgcICBAAGIAEMgcICRAAGIAE0gEINjA5NGowajSoAhOwAgHiAwQYASBf&hl=en-US&sourceid=chrome-mobile&ie=UTF-8