@Oleksii
Here you go:

Mastodon – a microblogging/status posting software package that uses ActivityPub to federate between other instances of servers to form a mesh network of social media servers and services.
Fediverse – the nickname many have started calling this federated mesh network; it is a term that describes a network of social networks that can communicate with each other using open standards and protocols. The word Fediverse is a combination of “federation” and “universe”.
PubSub – Pub/Sub is a term that stands for publish/subscribe, which is a design pattern for asynchronous communication between different components or services in a distributed system.