Wiktionary
on-base plus slugging
n. (context baseball English) A metric used to evaluate the effectiveness of a hitter; the sum of on-base percentage and slugging percentage.
Wikipedia
On-base plus slugging
On-base plus slugging (OPS) is a sabermetric baseball statistic calculated as the sum of a player's on-base percentage and slugging average. The ability of a player both to get on base and to hit for power, two important offensive skills, are represented. An OPS of .900 or higher in Major League Baseball puts the player in the upper echelon of hitters. Typically, the league leader in OPS will score near, and sometimes above, the 1.000 mark.