What is topic in FCM?

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Tags

1. #devices
2. #model
3. #publish
4. #based
5. #messages
6. #right
7. #opted
8. #multiple
9. #compose
10. #subscribe
11. #reliably
12. #delivering
13. #routing
14. #messaging
15. #needed
16. #allows
17. #handles
18. #message
19. #particular
20. #topic