Fediverse

The Fediverse is a network of social networking platforms that connect to each other.

Accounts from one smaller social network (specifically in a server) is capable of interacting with an account from another totally distinct social network.

The concept that one service (such as a social networking site) is capable of interacting with other services that serve similar intents is known as federation. Hence the name "fediverse", which is a portmanteau of the words "federated" and "universe", thus "federated universe", or more compactly "fediverse".