The Fediverse (commonly shortened to fedi)[2][3][4] is a collection of social networking services that can communicate with each other (formally known as federation) using a common protocol . Users of different websites can send and receive status updates, multimedia files and other data across the network. The term Fediverse is a portmanteau of federation and universe.[5]

The majority of Fediverse platforms are based on free and open-source software , and create connections between servers using the ActivityPub protocol. Some software still supports older federation protocols as well, such as OStatus, the Diaspora protocol and Zot, while newer protocols such as AT Protocol connect via network bridges. Diaspora is the only actively developed software project classified under the original definition of Fediverse that does not support ActivityPub.[6][7]
Design

While a traditional social networking service will host all its content on servers managed by the owner of the website, the decentralized structure of the Fediverse allows any individual or organization to host a social platform using their own servers (referred to as an "instance").

https://en.wikipedia.org/wiki/Fediverse