/kbin meta

Hi there! So I'm two weeks in to kbin and I think I have a layman's understanding of the fediverse, but I'm still not the most technical person, so I thought I'd just post my questions here.

So I know "fediverse" stands for federated universe, so does "kbin" also stand for something? I tried checking the FAQ but the about page just tells me it's a link aggregator, and google links me to a Japanese manufacturing site or those birth name meaning/ancestry sites. (can anyone tell me if lemmy also stands for something or is this just a word the developers came up with?)

Regarding defederation, does it affect previous posts? If there's a thread with comments by multiple people under different instances, does defederating break the chain?

In fact who "owns" a thread? Like, in which instance is it stored? If someone posts on kbin, and people from lemmy and beehaw comment on it, does kbin "keep" all of those stored away or do they stay in their respective instances?

And am I correct in thinking that instances who defederate essentially block off an instance, but that instance can still see their posts, but not interact? ie. Instance A defederates from B, so they can't see/interact with B, but B can still see A but not interact with them? Or is it a mutual blocking? Ergo they both can't see nor interact. I know beehaw defederated with lemmy recently, so...?

The whole concept of defederating is just so interesting to me. I know I have to read more about it but those were mostly my main questions.