The Collaborative International Dictionary
Slugging average
Slugging average \Slug"ging av`er*age\ (Baseball) a measure of the effectiveness of a batter at reaching base and advancing other runners, calculated as the sum of the number of bases reached on each hit, divided by the total number of times at bat. A double counts two bases, a triple three, a home run four. Thus a batter with four singles, two doubles and a triple in 20 official times at bat would have a slugging average of 0.550, and a batting average of 0.350. Also called slugging percentage. Compare batting average.
Wiktionary
slugging average
n. (context baseball English) A statistic which compares the total number of bases achieved by a batter over that batter's number of at bats.