What does reach and impressions mean on Instagram?

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Tags

1. #reach
2. #matter
3. #people
4. #think
5. #clicked
6. #total
7. #content
8. #displayed
9. #delivered
10. #impressions
11. #impression
12. #however
13. #someone
14. #number
15. #unique
16. #times
17. #means