From BR Bullpen
While the minor league classification system is rather clear, there has been a problem with the A designation for some time, as it covers three kinds of leagues. Some, like the New York-Penn League, are short-season leagues for players beginning their professional careers. Others, like the Midwest League, are for players with some pro experience but getting their first look usually at a full five-month-long season. Still others are a step above that, as players have been weeded out who failed that tier. This step is known informally as A-Advanced or High Class A or Advanced Class A or similar titles. These leagues, a step below AA, are presently the Carolina League, California League and Florida State League.