Playoffs are normally played between teams that finished well during the regular season. Professional leagues that hold playoffs are usually divided into geographically based groupings of teams, usually called divisions, but sometimes called conferences (and sometimes, divisions are collected into a higher groupings that are then termed conferences. Generally, during the regular season, teams play more games against opponents that are within their own division than those outside the grouping. The teams that finished in first place within their division at the end of the regular season are are eligible to participate in the playoffs. In addition, teams that finished second or even lower in the standings are often added to the tournament; these are known as wild card teams. Some leagues have also held playoffs between teams that were tied for first place, although the NFL instead uses a complicated tie-breaking formula to resolve this situation.
Playoff games have evolved over the years, involving increasing numbers of teams in larger tournaments. This both increases the excitement for fans, and also increases revenues for the league. The notion of a post-season championship in modern professional sports was instituted by professional baseball with its World Series games between the champions of the American League and the National League. The leagues themselves were not divided into divisions and did not have playoffs unless there was a tie for first place (the team finishing first in the league was said to have 'won the pennant'). The NFL divided its teams into divisions in 1933 and began holding a single playoff championship game between division winners. In 1967, the NFL expanded and created four divisions, which led to the institution of a larger playoff tournament. After the merger with the American Football League, the NFL began to use a single wild card team in each conference in its playoffs, in order to produce eight contenders out of six divisions; this was later expanded so that more wild card teams could participate. Major league baseball also expanded at the end of that decade and created divisions in each league, which led its first use of regular post-season playoffs to determine league champions. Further expansion by baseball led to its own adoption of the concept of wild card teams.
The NHL has traditionally opened up its playoff games to a much larger number of teams, including those with a losing record.