Professional sports leagues are organized in numerous ways. The two most significant types are one that developed in Europe, characterized by a tiered structure using promotion and relegation in order to determine participation in a hierarchy of leagues or divisions, and a North American originated model characterized by its use of franchises, closed memberships, and minor leagues. Both these systems remain most common in their area of origin, although both systems are used worldwide. Etymology The term league has many different meanings in different areas around the world, and its use for different concepts can make comparisons confusing. Usually a league is a group of teams that play each other during the season. It is also often used for the name of the governing body that oversees the league, as in America's Major League Baseball or England's Football League. Because most European football clubs participate in different competitions during a season, regular-season home-and-away games are often referred to as league games and the others as non-league or cup games, even though the separate competitions may be organized by the same governing body. Also, there is a rugby football code called rugby league, which is distinct from rugby union. Structure of North American leagues (Franchise and minor league system) Professional sports leagues in North America comprise a stipulated number of teams, known as franchises, which field one team each. The franchises have territorial rights, usually exclusive territories large enough to cover major metropolitan areas, so that they have no local rivals. New teams may enter the competition only by a vote of current members; typically, a new place is put up for bid by would-be owners. The "franchise system" was introduced in baseball with the formation of the National League in 1876 and later adopted by the other North American leagues. Although member teams are corporate entities separate from their leagues, they operate only under league auspices. North American teams do not play competitive games against outside opponents. The leagues operate in a closed membership system and do not have promotion and relegation. It is organized in a way that assures the teams' continued existence in the league from year to year. On occasion a league may decide to grow by admitting a new expansion team into the league. Most of the teams in the four major North American leagues were created as part of a planned league expansion or through