ActivityStreams 2.0 is the data format underlying ActivityPub. It provides a JSON-LD vocabulary for describing social interactions: creating, liking, sharing, following, and other activities that occur in federated social networks.
The specification defines a core set of activity types (Create, Update, Delete, Follow, Like, Announce, and others) along with object types (Note, Article, Image, Person, and others) that activities act upon. Implementations extend the vocabulary as needed while maintaining interoperability through the shared JSON-LD context.
ActivityStreams 2.0 was standardized by the W3C in 2017 as part of the Social Web Working Group’s suite of recommendations.