The National Football League is a professional American football league consisting of 32 teams, divided equally between the National Football Conference and the American Football Conference. The NFL is one of the four major professional sports leagues in North America, the highest professional level of American football in the world, the wealthiest professional sport league by revenue, and the sport league with the most valuable teams. The NFL's 17-week regular season runs from early September to late December, with each team playing 16 games and having one bye week. Following the conclusion of the regular season, seven teams from each conference advance to the playoffs, a single-elimination tournament culminating in the Super Bowl, which is usually held on the first Sunday in February and is played between the champions of the NFC and AFC. The NFL was formed in 1920 as the American Professional Football Association before renaming itself the National Football League for the 1922 season. After initially determining champions through end-of-season standings, a playoff system was implemented in 1933 that culminated with the NFL Championship Game until 1966.