X rating
In the original Motion Picture Association of America film rating system, X rating represented that no one under 18 should be allowed to enter. Unlike the others, this rating was not copyrighted, and the rating became tied to pornography. Many theaters chose not to take an X rated movie, and many newspapers would not run ads for them. Certain movie companies had to release their films without rating, in particular independent movies. In Autumn 1990 the X was replaced with NC-17, but over the years, NC-17 absorbed the same stigma that the earlier X rating had.