No... what they mean is that the game has a set of rules. These rules are designed around the ability to provide a fun and challenging game. The balance is between the fun and the challenge. A game that is too difficult is a lot of times not seen as fun (especially if it is impossible) and a game that is seen as easy is a lot of times seen as fun (especially if you get a sword of godly power and get to pound people into the ground all the time).
Of course there are impossible situations where the fun is to see how long you can survive, but if the game was not balanced that would mean I could make it last 2-3 days before you are overwhelmed or 1 - 2 seconds.
I could take every monster unit in the game and give them all the hitpoints of some mites and the initiative of a turtle to boot. Won't change any abilities or rewards. You would find the game fun for awhile, but is this a balanced level of play. The game is too easy, but hey I would have fun watching my militia kill a storm dragon and can have lots of fun doing it.
Seconding I could set every monster unit to have an initiative of a rabbit and the hitpoints of twice that of any of the titans. Give every unit damage in all aspects, be it fire, cold, poison, and so forth. But if I don't change your hitpoints to match or damage to compare, it would be an impossible game to play. In fact, why not just have it in the scripts that every player starts directly next to 8 storm dragons.
So the term balance does not refer to nerf things, sometimes it refers to that other things needs to be brought up to the awesomeness. Under particular reasonable conditions a simple dagger shouldn't be able to kill a dragon on the first turn. (Not talking about a dagger of dragon slaying, but a simple rusty level 1 dagger). That would probably mean that the simple dagger needs to be nerfed or the dragon needs to be buffed. In essence, there is a correct point where fun and challenging meet. This balance is impossible to acheive with everyone and this is why you will never please everyone.
Thus, the other part of balance is within the playing community. Give enough fun element to the majority while not completely shunning the minority. This is usually achieved by difficulty settings, if I put it on Insane I should expect a challenge, and if I set it to easy it should be closer to I WIN senario everytime. But you can't have a slider for everything because then you might as well make your own game to play.