Mastodon is a “federated” social network that works like Twitter. It puts the control of data into the user’s hands, not in a single corporation.

Mastodon uses ActivityPub to make sure that each Mastodon instance can reach the others.

ActivityPub is also implemented by other applications such as PeerTube and Plume. This is what makes up the Fediverse: a collection of social networks that function as a single one.