reference to the server they usually post through
Roughly, yes. Imagine there isn’t just one reddit, but multiple reddits, all with their own users, sub-reddits and eventually even rules. Now all these multiple reddits can “talk” to each other. That’s why I’m on lemmy.zip and I can see a post someone hast posted on lemm.ee - that is federation. Saved on different servers, but looks like one coherent feed.
Defederation means that an admin of an instance excludes one or more instances from communicating with his. I’m not 100% sure what every implication is, but roughly, the instances can’t communicate with each other, so if lemmy.world defederates from lemmy.zip, for example, we could not have this conversation right now. You also would not see any posts from lemmy.zip and I would not see any from lemmy.world
Lmao what. Blahaj is just as bad as hexbear.