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: What about descriptions of associated networks, Stats / Nodes / Instances / Hubs, etc?
Fediverse visualization: https://kumu.io/wakest/fediverse
Generalistic and moderated instance.