An administrative announcement.
Q: What's this "Federation thing?"
A: A bunch of communities, on different servers, sharing /some/ but not necessarily /all/ of their traffic. Or, in some cases, none. It depends.
The User Guide has a good section:
Q: Does Federation -- different sites and even networks interconnecting -- mean that there might be the same username in different places?
A: Yes. It's a lot like email in that regard. "rosa.martinez" might exist on, say, Gmail, Hotmail, and Yahoo, but be three separate people. Or two the same and one different. You've got to check.
Generalistic and moderated instance.