What does brackets mean in regex?

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Tags

1. #group
2. #quantifier
3. #limits
4. #inside
5. #square
6. #round
7. #character
8. #expression
9. #together
10. #braces
11. #define
12. #specific
13. #brackets
14. #curly
15. #placing
16. #regular
17. #parentheses
18. #class