ELI5

The Fediverse is a network of services. It is an agreement to communication between platforms.

Services can be groups of services with different themes and types of content.

Some people may create text-only services. They split into three groups of people, and each group hosts their own services that join the Fediverse. They then link each other and share their content and users. You can see and subscribe to and talk with users of the other servers.

Another group thinks text-only is stupid. They create a service that only hosts images. No text allowed. They join the Fediverse too.

Now both groups services are part of the Fediverse. They communicate and share content through the same kind of protocol, the same kind of agreements.

But does it make sense to mix text-only and picture-only services? Those that initially set out to create either may want a pure experience. They may present a split and separate experience to their users. But others may like both approaches, for an intentional, interesting form of content and discussion. They may create a service that combines the other two. In it, you can see and participate in both of the other kinds of services.