The advantage a team has over its opponent by playing at home in their arena in front of the local fans. Home ice advantage is a term most often used in the context of a best-of-seven playoff series, where the higher ranked team of the two participating in the series plays an extra game at home.
In a seven-game playoff series, the higher ranked team gets to play four of the seven games in their home arena and thus has home ice advantage over their opponent. Under the modern NHL playoff format, the team with home ice advantage plays games 1, 2, 5 and 7 in their home arena, and their opponent plays games 3,4, and 6 in their arena. The modern NHL playoff format allows the top eight teams from each conference to participate in the playoffs after the regular season has ended. The teams finishing first through fourth in each conference receive home ice advantage. However, if a lower seeded team wins the first game of a playoff series, it is said that this team has "stolen" home ice advantage because at that point, both teams have three home games left and the lower seeded team has a 1-0 advantage in the series.
Having home ice advantage and playing at home is important to teams because they would not need to travel as much, they would be sleeping at home and not in hotels, they would be able to spend time with their families, and they would be playing in front of their fans in their home arena. However, playing at home in the playoffs can have a few disadvantages, such as distractions and players being too much in their comfort zone. For this reason, a some NHL coaches decide to make their teams sleep in a hotel even when they are playing at home, so that they focus only on the hockey games.