The major professional sports leagues in the United States and Canada are the highest professional competitions of team sports in the United States and Canada. The four leagues universally included in the definition are Major League Baseball (MLB), the National Basketball Association (NBA), the National Football League (NFL), and the National Hockey League (NHL). Other prominent leagues include Major League Soccer (MLS) and the Canadian Football League (CFL).The NFL, NBA, MLB, and NHL are commonly referred to as the "Big 4". Each of these is the wealthiest professional club competition in its sport worldwide, and along with the English Premier League they make up the top five sports leagues by revenue in the world. In addition, the sports of these four leagues were all developed in their modern forms in North America, and all except American Football have become popular internationally. The best players from these leagues often become cultural icons in both countries because the leagues enjoy a significant place in popular culture in the U.S. and Canada.The NFL has 32 teams, and the others have 30 each. The vast majority of major league teams are concentrated in the most populous metropolitan areas of the United States and Canada. Unlike the promotion and relegation systems used in sports leagues in various other regions around the world, those clubs in the North American sports leagues remain static from season-to-season, unless they are disbanded or relocated. Each Big Four league, as well as Major League Soccer and the Canadian Football League, averages at least 15,000 fans in attendance per game as of 2013.