Kbin is the software that runs the instance. Kbin.social is the instance (running on Kbin) run by its developers. Instances in the Fediverse can run on multiple types of content management frameworks, the most popular of which is Lemmy.
When an instance defederates from another instance, it stops talking to it. It stops reading and copying the defederated instance's posts and comments. The posts still exist on the original instance, and if posted before defederation, still exists on the copying instance. However, the two copies are no longer connected, so if someone posts a comment on the original post in the original instance after defederation, the defederated instance will not see it. Likewise if someone posts a comment on the copy of your post on the defederated instance, it will only be available on that instance, and not copied back to your original post on the original instance.
Essentially, the content fragments into two copies when defederation occurs, with each separately hosted and no longer in synch in terms of likes, boosts and comments.
I'm uncertain whether defederation is always a two way street. It's my undertanding that if instance A defederates from instance B, instance B can still read A's content unless it chooses to defederate from A as well. However, as instance A isn't accepting input from instance B, nothing that happens on instance B (comments, likes, boosts) will be shared with A.
DrChickenbeer
limecyanide