I believe the letters stand for "Federal Communications Commission," but don't quote me on that. They're an organization that basically decides who can say what on what medium. An extremely dumbed-down example can be found in Nickelodeon's supremely mediocre Fairly OddParents, specifically in the episode where Timmy starts a radio station. The FCC then comes to arrest evil babysitter Vicki for saying the word "idiot," which is only permissible to say on TV, on the radio. Which is extremely dumbed down and not quite Nazi enough, but basically it's accurate.