movies

I remember the created NC 17 for tv when became adult.

NC-17 predates the TV ratings system by six years: NC-17 for movies was introduced in September 1990, and the TV parental guidelines introduced in December 1996. The equivalent rating for television to NC-17 is TV-MA.

But for me you say X then you are saying a porno.

This is actually why NC-17 was created by the Motion Picture Association of America in 1990. For decades X was “no children allowed,” but X wasn’t copyrighted by the MPAA and it was eventually co-opted by the pornography industry, as you mentioned. The MPAA still needed something for wider-audience films that weren’t pornographic.

There were a lot of X-rated films in the 60s, 70s, and 80s that were rated X but weren’t pornographic. Midnight Cowboy, The Evil Dead, and A Clockwork Orange, for example, were all rated X on release. None are pornographic but probably shouldn’t be seen by children.

The Wikipedia page on the X rating and the MPAA rating system in general has more info.