What are the National League and American League in Major League Baseball?

They are the 2 overarching leagues that comprise all of Major League Baseball (MLB). There are 15 teams per league and within each league, there are 3 divisions (west, central, and east). The rules are consistent between the leagues (though that was not the case as recently as a few years ago until the NL adopted the designated hitter rule). Following the 162-game regular season, there are playoffs in each league. The winner of the American League and the National League have won the pennant for their respective league. They then play against each other in the World Series to determine the championship team of the season.