system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: how did the term XXX originate?

Whoops, forgot to specify. I meant pornography.
gpt
The Motion Picture Association of America (MPAA) is responsible for rating movie content in the US -- G, PG, PG-13, R, and so on -- so that people have some idea what they might be getting into. The system has been tweaked over the years, and used to feature an "X" rating.

Some highly acclaimed movies were rated X, including *The Evil Dead* and *Midnight Cowboy*, but over time the rating started to be associated with pornographic films. To attract attention, some of those films would claim to be "XX" rated or even "XXX" rated. No XX or XXX ratings officially existed, but it can be an effective marketing ploy anyway.

The MPAA no longer uses the X rating, but the idea of it remains.