The Stanley Cup playoffs is an elimination tournament in the National Hockey League consisting of four rounds of best-of-seven series
Eight teams from each of the two conferences qualify for the playoffs based on regular season points totals. The final round is commonly known as the Stanley Cup Finals, which sees the two conference champions play for the Stanley Cup.
The NHL has always used a playoff tournament to determine its champion. Its playoff system has changed over the years, from the leagues inception in 1917 when ownership of the Stanley Cup was shared between different leagues, to when the NHL took over the Cup in 1926, to the current setup today.
Source: Wikipedia