A perfect season is a sports season including any requisite playoff portion, in which a team remains undefeated and untied. The feat is extremely rare at the professional level of any team sport, and has occurred more commonly at the collegiate level in the United States. A perfect regular season (known by other names outside the United States) is a season excluding any playoffs, where a team remains undefeated and untied; it is less rare than a complete perfect season but still exceptional. A perfect season may be part of a multi-season winning streak.