A Party Game is a game mode in the Super Monkey Ball series. A Party Game, as its name suggests, is a multiplayer game which has nothing to do with the regular game.
There are also the three Mini Games (Monkey Billiards, Monkey Bowling, and Monkey Golf) that need to be unlocked with 2500 Play Points each. Although these are in a different category, these basically are Party Games.
In Super Monkey Ball 2, there are twelve party games. The first six are remakes of the original six (they end in 2 to represent this). The other six are brand new. They are Monkey Boat, Monkey Shot, Monkey Dogfight, Monkey Soccer, Monkey Baseball, and Monkey Tennis. The six new ones need to be unlocked with 2500 Play Points each, just like the Mini Games in Super Monkey Ball.