The story
Blend of federation + universe. The earliest known mention of fediverse on Twitter was in 2012. The earliest known use of fediverse by the W3C was in 2013.
First known use, by meaning
- from 2012 The distributed social media network of federated services using open standard communication protocols, especially ActivityPub and historically OStatus.
Etymology from Wiktionary, CC BY-SA 4.0.