"Culture" stands for the sociological traits a particular empire has. All empires have one - if you don't specifically select one in the game set-up, you end up with "neutral" by default. They're "free" points, in a sense, but they're usually a mix of advantages and disadvantages. In the unmodded game, they're not exactly evenly balanced. One of the list members here, Jourin, came up with a balanced culture file (you can find it
on this thread.)