The word fediverse is a combination of the words Federation, like federated nations, and Universe. It indicates that there is no single entity controlling the whole network. There are lots of diverse places like planets in a universe or like villages on a planet. Each may have different cultures, languages, interests, etc. but they are connected via a communication protocol (Activity Pub/OStatus) so that they can interact.
You already have an example of this with your telephone. You can communicate with people that are customers of other telephone companies without having to be a customer of each of them.
There are many fediverse social networks with different taste and goals.
Friendica's philosophy is to communicate with everybody. As of 2020, Friendica is able to communicate via ActivityPub, Diaspora*, OStatus, Twitter, RSS Feeds and several other protocols. So you don't need a lot of different tools, software or apps. You can just connect to your information sources and you will see that they appear in your timeline.