Our comrade Dessalines has great insight into the rise and fall of Reddit and where he expects Lemmy to fall in with the Fediverse and away from corporate social media
It’s a term that is newer than email, but accurately describes it.
You can create an email server for you and your buddies to send messages back and forth on. Beyond that, you can also send messages to people who use other email servers. Thus, email is considered “federated”.
Where you hear the term used more recently is with the concept applied to social media. Lemmy is a Reddit clone, and you can set one up for your buddies just like we did here. The only issue is that ours doesn’t support federation for semi-technical reasons (happy to explain), but that’s going to be fixed (later this year maybe)?
Once Hexbear had federation in place, we will be able to post to and interact with communities on https://lemmy.ml as well as https://lemmygrad.ml which are their own “instances” with their own rules and community. If people were to schism because they hate the mods or whatever, they could just set up their own instance with blackjack and hookers, but they wouldn’t be totally cut off from Hexbear (unless the admins blocked their whole instance from federation back for being toxic or Nazis or whatever).
Mastodon is the Twitter version of this btw.
A site gets to choose what other sites it federates with, just like you could block specific email addresses from sending you mail.