Balanced (see also: Fairness, Longevity)
A state in which a game can be played indefinitely by its entire community without developer interventions or player conventions.
There is no such thing as a “balanced game”.
This is not to say that there is no such thing as a perfectly balanced game, but that balance is not a quality of a game at all, but of the experience of playing a game. And since this experience depends on who is playing, a game can only be considered “balanced” for a specific group of players.
The latest 2d fighting game might be balanced when you and your friends are taking turns mashing buttons, but degenerate into ridiculous 100+ hit combos when mastered by a some over-zealous Japanese teenager. To be considered truly balanced, a game must go beyond this kind of local balance and be balanced for the entire game community.
In a similar way, it’s clear that any game may be balanced for brief periods of time. Often the most balanced point in a multiplayer game’s life-cycle are the first few nights after launch, before the community has discovered the optimal strategies, glitches and cheap tactics, before the unending train of patches and tweaks. So any useful definition of balance must also require the game experience to remain stable for a significant time.
Finally, balance requires a certain amount of independence and permanence. The purpose of balancing a game is to allow players to strategically plan and skillfully execute within an impartial system that they can predict. This does not happen if the game requires constant changes and tweaks, either by direct developer updates or community-endorsed “honor rules”.
Note: This definition of balanced does not require that a game be “fun” to be “balanced”.