An immediate problem is that "community" is a term in the threadiverse, where !fediverse@lemmy.ml is a community. It also might make it sound like an exclusive space with a specific topic, whereas in reality when you join a server you can still interact with the wider network.
IMO this is a concept that can't be expressed in one word when someone is unfamiliar with the concept. We put together this guide a while back to try and explain it: https://fedecan.ca/en/guide/get-started