Happy 10th birthday to the SABR/Baseball-Reference Encyclopedia. Thanks to all those who have contributed and welcome to any who wish to contribute.
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.