In Major League Baseball, a player earns the Triple Crown when he leads a league in three specific statistical categories.
When used without a modifier, the “Triple Crown” generally refers to a batter who has led the league in batting average, home runs, and run batted in (RBI). The Triple Crown epitomizes three separate attributes of a good hitter: hitting for average, hitting for power, and producing runs.
On October 3, 2012 Detroit Tiger Miguel Cabrera becomes the first Triple Crown winner since Boston’s Carl Yastrzemski in 1967. Cabrera finished with a .330 average, 44 home runs and 139 RBIs.
Source : Wikipedia entry