Reddit has subreddits. What does Lemmy go with?
My personal vote is for lemmings!
Edit: I am personally leaning towards Sublemmy now. It retains the context of being a forum under the general sphere of Lemmy and the connection to Reddit lets people know immediately what Lemmy is about. Thanks to @BurningnnTree@lemmy.one for the comment!
Officially they’re called communities, the issue with that is that when you’re trying to mention them in conversation with someone outside of Lemmy, you often have to use the longer “Lemmy Community.” Not the end of the world, but something quicker and more distinct might be better.