One of two components (alongside the National League) of Major League Baseball. Formed at the beginning of the 20th Century, it was briefly a rival to the National, before serious interleague warfare was resolved with a merger. Now there's little to differentiate the two leagues, except for the designated hitter, and they will perhaps be little more than a memory in a few years, as MLB continues its oft-pointless reorganization efforts.

Also an old school way to denote the American Hockey League; the NHL was called the "National League".