What does R mean in movies?

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Tags

1. #suitable
2. #adult
3. #suggested
4. #material
5. #guardian
6. #guidance
7. #under
8. #strongly
9. #rated
10. #parents
11. #accompanying
12. #parental
13. #audiences
14. #admitted
15. #parent
16. #cautioned
17. #requires
18. #children
19. #general
20. #restricted
21. #inappropriate