Was there ever a genuine meaning to the X, XX and XXX ratings on

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What did the 'X' stand for in the film rating that used to be call X-Rated? - Quora

What did the 'X' stand for in the film rating that used to be call X-Rated? - Quora

What is the meaning of a movie that has an XX rating? - Quora

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XXX - Rotten Tomatoes