wfz on 29 April 2012
Mature is the rating that describes the audience that is allowed to buy it. There are different things in different societies that people don't want their children exposed to, and if such things are in video games, they receive a higher rating to prevent them from exposing those elements to younger audiences.
Of course, since it's a suggested rating, and not legally binding, it doesn't do all that much to prevent it. But that's what it's for.
