Lemmy calls them "communities" but since Lemmy federates over ActivityPub which can have lots of different implementations and Lemmy can speak to them, they can have different names. For example there is kbin which calls them "magazines", another implementation might call them something else.
"Community" as the other replies already mentioned, but how do we abbreviate that? "Sub" worked well imho, but does "com" have the same ring to it?
Any better suggestions?
That'll work when typing things online, but not in f2f conversations. I thought about 'com(m)' which will work, typed out in certain contexts, but I think that sounds too much like other words in several languages including English to use in speech. But if you prepend 'lemmy' to that it's quite a distinguishable word that sounds like 'lexicon': lemmycom(m)!