What does mean in regex?

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Tags

1. #expression
2. #operation
3. #expressions
4. #strings
5. #while
6. #lowercase
7. #means
8. #shortened
9. #special
10. #description
11. #metacharacter
12. #match
13. #representing
14. #regex
15. #pattern
16. #search
17. #matched
18. #regular
19. #instance