Game-balance is something often mentioned in roleplaying games. The idea comes from the world of boardgames/ strategy games (and later computer games), and the purpose is to make sure that units of different kinds are balanced against each other.
In many roleplaying games there is also a discussion that different types of characters should be equally powerful. A lot of time is spent on comparing feats/ abilities/ attacks etc to make sure that no character accidentally becomes more powerful than another.
There are two aspects of "balance" in a roleplaying game I feel often are neglected, and perhaps more important than power in a combat.
First of all is the ability to influence the story and the scene. Even though I might not be a combat monster, all players and characters should have a fairly equal input and ability to push the story or scene in a specific direction.
Second, all characteers should have an equal time in the spotlight. I've been in situations where one character has 1 simple attack / round whereas other characters have multiple attacks and/ or familiars and summoned creatures. This means that the player with the single attack can resolve his round in 10-15 seconds whereas players with a number of exotic attacks (with creatures etc) can take up to 3-5 minutes to solve his round.
For me, these two aspects, influence and time, are more important balancing factors than actual combat balance.