ActivityStreams 2

ActivityStreams 2.0 is the W3C standard for encoding social interactions and metadata using a JSON-LD based syntax.

This protocol provides the foundational vocabulary for the decentralized web, powering major platforms like Mastodon and the broader Fediverse via ActivityPub. It defines a model for representing 'Activities' (such as Post, Like, or Follow) performed by 'Actors' on 'Objects.' By utilizing JSON-LD, it ensures that data remains machine-readable and extensible across different servers, enabling seamless cross-platform communication for millions of users.

https://www.w3.org/TR/activitystreams-core/