It's a collection of features meant to sit on top of ActivityPub.
ActivityPub is a general protocol for decentralised social networking. Instead of Facebook or Twitter servers generating a feed for each user, user's servers send updates to each-other.
I think the audience is expected to know about distributed systems and the fediverse. Think of it like being linked to https://luajit.org/ without knowing anything about lua, programming and so on. Some links on HN are pulled from places where certain knowledge is pre-assumed.
ActivityPub is a general protocol for decentralised social networking. Instead of Facebook or Twitter servers generating a feed for each user, user's servers send updates to each-other.