"It is a common name for federated social networks running on free open software on a myriad of servers across the world. Historically, this term has included only microblogging platforms supporting a set of protocols called OStatus. With the wide adoption of a new standard protocol called ActivityPub, many new projects appeared. This guide unites all interconnected networks under one term."
https://fediverse.party/en/fediverse
(via @privatechitizen)