don't lose your head over this. lemmy, kbin, mastodon and apparently threads (the new twitter alternative by facebook/meta) are all part of the fediverse, which means they all follow a decentralised approach. mastodon and threads are microblogging platforms, while kbin and lemmy have a similar format to reddit. because they are all part of the fediverse, all these platforms communicate with each other and you can use kbin to subscribe to microblogs such as mastodon and have them appear in your feed. defederation basically means cutting the link between one server and another, so they can't communicate anymore.