@Ninguem It is a kind of forum, but not quite as structured. The special thing for me is that it is part of the Fediverse. For me, it is a platform that offers a topic-centred access to the Fediverse. It follows a different logic than microblogging services like Mastodon, which are account-centred and in which the content has to be structured by the individual users via lists, hashtags, antennas and the like.
It is possible to interact with Lemmy content from Mastodon etc. and also to create posts in Lemmy communities (I’m replying here from #Friendica)). But with Lemmy account (which I also have) the content is of course even better structured. But it is not quite as structured as in a classic forum.