Originally inscribed the Dominion Hockey Challenge Cup, the trophy was donated in 1892 by Lord Stanley of Preston, then–Governor General of Canada, initially as a "challenge trophy" for Canada's top-ranking amateur ice hockey club. The champions held onto the Cup until they either lost their league title to another club or a champion from another league issued a formal challenge and defeated the reigning Cup champion in a final game to claim their win.
The Stanley Cup was first awarded to the Montreal Hockey Club in 1893 when the team won the 1893 AHAC season. The team then had to defend its champion-title both through league championships and challenge games organized by the Stanley Cup trustees. Until 1912, these challenges could take place before or during a league season. After 1912, the trustees ordered that challenges only take place after all league games were completed.
The NHL has changed its playoff format several times since 1927, and thus the final round has not always pitted conference or division playoff champions against each other. In the playoff format used from 1929 to 1938, the two teams with identical division ranking would face each other (i.e. the first-place teams played each other, the second place teams play each other, and likewise for the third place teams).
The winner of the first place series would automatically advance to the final round. The winner of the second and third place series would then play each other, with the winner of that series earning the other berth to the championship round.
During the Original Six era, the top four teams made the playoffs, with the first and third place teams battling in one semifinal series, while the second and fourth place teams battled in the other. And from 1975 to 1981, all the playoff teams were seeded regardless of division or conference.
From 1982 to 2020, the NHL's final round pitted the league's two conference playoff champions. In 2021, the four playoff division champions will be re-seeded and play in the Semifinals, with the winners of those series advancing to the Finals. The league is expecting to return to the previous conference based playoff format in 2022.
According to en.wikipedia
