"I've already answered this Yoshi."
Balance is simply what it is. An equal amount of light and dark. Good and Evil. Greed and selflessness. Love and Hate. Poor and Rich. It goes on for quite some time. We make sure that what we do will insure to keep an equal balance of these things.
Take the city states for example. Demacia and Noxus. One city that thrives to make sure that their is always good abound it's streets. The other thrives off of strength and power, where anyone will do what they must to achieve greatness.
Piltover and Zaun is another example. Both are technologically advancing states, yet Zaun hasn't always done the cleanest, and environmentally friendly approach. Piltover on the other hand, tries to do the opposite, in which their city is progressing, and is staying at a rather clean rate.
As you may also notice, Piltover is allied with Demacia, as is Zaun with Noxus. Two cities of light, and two cities of dark. It is an equal amount as you may notice, as Bandle and Ionia are more of a neutral you could say.
That is all I can say for now without giving out too much information.
-The Eye of Twilight