Seeing some push back here on the idea of confusing things with more terms than just "fediverse". I get that. The problem is that that cat is very much out of the bag. Surely, for the vast majority of people that have any awareness of the fediverse, they think it's just Mastodon.
Either way, "Mastodon" is a much larger "brand" than "fediverse" or anything else on the fediverse. So trying to get some conceptual branding going makes sense. It make things more clear, as the idea of the fediverse itself is kinda fuzzy and complex and probably best left out at the beginning. It's a little bit like the matrix, you have to see it with your own eyes, IMO.
So, my lame contribution ...
Threadiverse!: "Social media, but woven into threads, like Reddit or Forums, not like the chaos of Twitter, but all on the Fediverse so you can find anyone else doing anything else too."