Whet did "High-A" come in to being and what does it mean?
From MLB.com ...
Low/High-A Ball:
A-ball is the first step toward playing a legitimate professional season as a baseball player. It's where players first have Spring Training and prepare themselves for a 140 game season stretching just over 5 months. Players coming straight out of high school are usually assigned to Low-A while college players, especially ones who come out of major college programs, can start their first full season at High-A.
Other levels ...
Rookie Ball/Short Season:
The MLB draft happens in the middle of the major league season, so a lot of younger players aren't ready to hop into the middle of an ongoing season, especially players drafted straight out of high school. That's what the short season, or rookie ball season, is for. Short season ball is meant to let newly drafted players get acclimated to the life of a major league ballplayer, with varying degrees of travel involved. For example, the South Atlantic League is one without a whole lot of rigorous travel involved, which works best for players just coming out of high school or for international players acclimating to the United States for the first time.
Double-A Ball:
Double-A baseball is where you'll find a lot of talent. Since it's one step closer to the major leagues, it weeds out a lot of players who don't make the cut talent-wise. At the same time, the amount of talent it takes just to get to Double-A is such a high bar that anyone making it even to this level has major league potential. Double-A is also known as the beginning of the 'upper minors'. Since the competition is so much better, pitchers are usually a lot more advanced than those at Single-A. Double-A pitchers are usually the ones talented enough to not only have the pitching ability to succeed, but the mental preparation to get the most out of that talent, and the same goes with the hitters at this level. Sure, you'll find players with major league experience at the Double-A level, but more often than not this level is full of players who are still ascending to the majors.
Triple-A Ball:
The closest level to the majors, Triple-A is filled with all kinds of players. Some are the game's rising stars, although some of the best players can skip Triple-A and move directly from Double-A to the major leagues. Triple-A is also full of players who have major league experience, some of them having quite a bit of it, as well as established major league players that are rehabbing from injuries that have kept them out of action for an extended period of time. With the combination of old and new stars as well as the occasional major leaguer or two, Triple-A baseball is a fan-favorite place to see all kinds of fan favorite players.
With over 240 minor league teams across the nation, there's a chance one plays closer to you than you think. With lower prices and elite talent at every level, minor league games are a great way to get a live baseball fix without breaking the bank.