Algorithms or methods to produce events or behavior that is random in nature.

Not to be confused with the Super User moderator, no matter how appropriate.
Random variance is a very common component of many games. From calculating the amount of damage dealt, to determining what opponents will be faced, to constructing entire dungeons through procedural generation, randomness is a spice that creates variety in a playing experience.

There are many ways to apply random calculations to a game, and the level of emphasis can greatly alter how strategy and gameplay evolve.