What does the green dot mean on Google Hangouts?

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Tags

1. #turned
2. #their
3. #notified
4. #setting
5. #picture
6. #messages
7. #invitations
8. #hangouts
9. #available
10. #immediately
11. #someone
12. #people
13. #about
14. #green
15. #classic
16. #video
17. #these
18. #profile