Minor League Baseball
Minor league baseball is a hierarchy of professional baseball leagues in North America and South America that compete at levels below that of Major League Baseball
. All of the minor leagues are operated as independent businesses, and many are members of Minor League Baseball
, an umbrella organization for leagues that have agreements to operate as affiliates of Major League Baseball.
Triple-A leagues usually hold many of the remaining 15 players of the 40-man major league roster whom the major league club has chosen not to play at the major league level. It has recently been referred to as a "spare parts" classification, because frequently a player who is good enough for the majors (especially if he had signed with a team needing someone to play his natural position) is held in reserve at the minor league level for major league emergencies.
There are currently three leagues in this classification: Eastern League, Southern League, and the Texas League.  Some players will jump to the majors from this level, as many of the top prospects are put here to play against each other, rather than against minor and major league veterans in Triple-A. A small handful of players might be placed here to start, usually veterans from foreign leagues with more experience in professional baseball. The expectation is usually that these players will be in the majors by the end of the season, as their salaries tend to be higher than those of most prospects.
Single A, or "Class A," is a classification comprising two subclassifications: Class A-Advanced and Class A. Players usually have less experience or have particular issues to work out; pitching control and batting consistency are the two most frequent reasons for a player to be assigned to Class A baseball.