As I understand it the "N" stands for "naughty" meaning it contains sexual situations that are inappropriate for anyone under age 18 to read.

"Let us remember that there is a creative force in this universe, working to pull down the gigantic mountains of evil, a power that is able to make a way out of no way and trasform dark yesterdays into bright tomorrows. Let us realize the arc of the moral universe is long, but it bends toward justice."
-- Martin Luther King Jr.