In game design, balance is the concept and the practice of tuning a game's rules, usually with the goal of preventing any of its component systems from being ineffective or otherwise undesirable when compared to their peers. An unbalanced system represents wasted development resources at the very least, and at worst can undermine the game's entire ruleset by making important roles or tasks impossible to perform.
Balancing does not necessarily mean making a game fair. This is particularly true of action games: Jaime Griesemer, design lead at Bungie, said in a lecture to other designers that "every fight in Halo is unfair". This potential for unfairness creates uncertainty, leading to the tension and excitement that action games seek to deliver. In these cases balancing is instead the management of unfair scenarios, with the ultimate goal of ensuring that all of the strategies which the game intends to support are viable. The extent to which those strategies are equal to one another defines the character of the game in question.
Simulation games can be balanced unfairly in order to be true to life. A wargame may cast the player into the role of a general who was defeated by an overwhelming force, and it is common for the abilities of teams in sports games to mirror those of the real-world teams they represent regardless of the implications for players who pick them.
Player perception can also affect the appearance of fairness. Sid Meier stated that he omitted multiplayer alliances in Civilization because he found that the computer was almost as good as humans in exploiting them, which caused players to think that the computer was cheating.
Video games often allow players to influence their balance by offering a choice of "difficulty levels". These affect how challenging the game is to play.
In addition to altering the game's rules, difficulty levels can be used to alter what content is presented to the player. This usually takes the form of adding or removing challenging locations or events, but some games also change their narrative to reward players who play them on higher difficulty levels (Max Payne 2) or end early as punishment for playing on easy (Castlevania).
Difficulty selection is not always presented bluntly, particularly in competitive games where all players are affected equally and the standard "easy/hard" terminology no longer applies. Sometimes veiled language is used (Mario Kart offers "CC select"), while at other times there may be an array of granular settings instead of an overarching difficulty option.