Championship Format
Like predecessor leagues, the champion of the NHA league since its founding was the team with the best regular season record, with a playoff only used if more than one team had the best win-loss record. This changed in 1917 with the invention of the split-season, whereby the champion became the winner of the annual playoff. The NHL continued the split-season and playoff format upon the winding up of the NHA organization. Except for the 1919–20 season, where there was no playoff because Ottawa won both halves of the season, the champion of the NHL has been the playoff champion.
The NHA champion was awarded the O'Brien Cup. This was continued by the NHL. Until 1927, the NHL champion was awarded the O'Brien Cup, supplemented by the Prince of Wales Trophy, starting in 1925. To win the Stanley Cup, the NHL champion had to play off in a "world's series" with the champion of the Pacific Coast or Western hockey leagues. After 1927, the NHL playoff champion was awarded the Stanley Cup, while the O'Brien Cup and Prince of Wales Trophy were reused as division championship and playoff runner-up awards.
Read more about this topic: List Of NHL Seasons