Definition of slugging percentage in English:

slugging percentage

noun

Baseball
  • A weighted average used to measure a batter's performance, calculated by dividing the number of bases gained on hits by the player's total number of at-bats.

    This average does not include bases gained by a hitter on walks; it is thus frequently considered in tandem with on-base percentage.

Origin

Early 20th century; earliest use found in The New York Times.