Party games are games which share several features suitable to entertaining a social gathering of moderate size.
The number of participants is indefinite and fairly large. Traditional multiplayer board games tend to accommodate anywhere from four to six or seven players at most, whereas party games generally have no fixed upper limit. Some games become unwieldy if more than twelve or fifteen play, but even for these the upper limit is flexible. Many party games simply divide everyone into two roughly equal teams.
The players can take part at varying levels. Not everyone enjoys straining themselves to the utmost to win, so good party games have multiple ways to play along and contribute to everyone's enjoyment. For example, in Fictionary not everyone needs to create plausible dictionary definitions; humorous submissions are at least as welcome. In Charades, players can actively participate in guessing without taking a turn at acting.
Player elimination is rare. Monopoly makes a poor party game, because bankrupt players must sit out while the remaining players continue. In contrast, no matter how far behind a team is in Pictionary, all players can participate until the very end.