So Lemmy is an instance and kbin is an instance as well. Think of them as reddit as a whole. On kbin subreddits are called magazines. Idk how it works on Lemmy so much.

From my understanding threads can be federated between Lemmy and kbin. In other words you can subscribe to Lemmy "sub reddits" on kbin and visa versa. Kbin also let's you microblog in a magazine which is kind of like a tweet?

That all being said I may be wrong about some of that or have the terminology wrong so if anyone wants to correct me feel free haha