Personally that term makes me a bit uneasy. To me it sounds too grandiose and organized just for something that might just be some random people shitposting or chatting about their interests. And actually having tight knit communities can easily lead to all kinds of negative effects, group think, hierarchies and drama.
Of course some subreddits, forums, lemmy communities etc can be actual communities but just as a personal preference I don't like the idea of calling them that default.
To me subinstance sounds more like a technical term, but I guess people would just call them subs anyway. I think that's a problem in general with deriving anything from "instance".
I guess community does a good job at being a more human centric term. You have the technical side of things, servers and software (instances) and on those you have the actual user facing parts (communities) so in that way it's kinda fitting.
Further overthinking about the terminology I just realised that Lemmy calls joining communities "subscribing" and Reddit calls it "joining", while I would naturally think it would be more fitting the other way around. Naming things is hard.
I think "sub" is what people are going to call them reguardless. It is just internet language at this point, a subdivision of a community (by community I mean lemmy as a whole) is called a sub. Weather it's a subreddit or sublemmy. I'm not saying bring reddit with us, I am just saying the internet can take the term "sub" with it and use it elsewhere.
For now. Commercial servers are possible, especially if communities become multi-instance in the future.
Every mature decentralized service calls them providers. Phone providers, ISPs, email providers, etc. I guess usenet just calls them "news servers", though.
if there different "linux" communities on different instances? does this mean i have to subscribe to all of them? is there a way to see all content from communities called "linux" from different instances?
or does each "linux" community simply fight for critical mass to become the "main" linux community on lemmy?
I don't dislike the idea that there could be multiple similar communities (for example Linux communities) on different instances. That way if you have beef with one you could sign up to another; in a non-ideal world that strikes me as healthier than having one to rule them all and lots of people bitter about it. I think it's best to leave it to sort itself out organically.
There could be different linux communities on different instances, and to see them all you'd have to subscribe to them and sort by subscribed view. But yeah, in practice most of the time there will emerge one "main" linux community and, if it gets big enough, likely offshoot communities for different philosophies or more specificity.