ActivityPub is a decentralized social networking protocol based on the ActivityStreams 2.0 data format. ActivityPub is an official W3C recommended standard published by the W3C Social Web Working Group. It provides a client to server API for creating, updating and deleting content, as well as a federated server to server API for delivering notifications and subscribing to content.

The ActivityPub protocol is a decentralized social networking protocol
based upon the ActivityStreams] 2.0 data format.
It provides a client to server API for creating, updating and deleting
content, as well as a federated server to server API for delivering
notifications and content.