Simplify the following text for a Grade 6 native English-speaking person.
Original: It refers specifically to the professional baseball clubs and leagues that are members of the National Association of Professional Baseball Leagues , Inc. and which ( other than Mexican League clubs ) have player development contracts with Major League Baseball teams .
Simplified: Minor league baseball is a level of professional baseball in North America . It is made up a many different teams which play in many leagues and levels of ability .