No, not in the MPAA rating system, but self-proclaimed X or XXX-rated films ae usually pornographic.
In the United States, the X-rating originally referred to a non-trademarked rating that indicated a film contained content unsuitable for minors such as extreme violence or explicit sex and thus was for adults only.
When the MPAA film rating system was instituted in 1968 in the U.S., the X-rating was given to a film by the MPAA if submitted to them or, due to its non-trademarked status, it could be self-applied to a film by a distributor who knew beforehand that their film contained content unsuitable for minors. In the late 1960s to mid 1980s, several mainstream films were released with an X-rating such as Midnight Cowboy and A Clockwork Orange.
Because the X-rating was not trademarked, anybody could apply it to their films, including pornographers, which many began to do in the 1970s. As pornography began to become chic and more legally tolerated, pornographers placed an X-rating on their films to emphasize the adult nature of them. Some even started using multiple X's (i.e. XX, XXX, etc.) to give the impression that their film contained more graphic sexual content than the simple X-rating. Nothing beyond the simple X-rating was ever officially recognized by the MPAA.
Because of the heavy use of the X-rating by pornographers, it became associated largely with pornographic films and thus non-pornographic films given a X-rating would have fewer theaters willing to book them and fewer avenues for advertising. This led to a number of films being released unrated sometimes with a warning that the film contained content for adults only. In response, the MPAA eventually agreed in 1990 to a new NC-17 rating that would be trademarked and thus could only be applied by the MPAA itself.
https://en.wikipedia.org/wiki/X-rated#United_States
