good description of Federation and Decentralization

"A decentralized service can reside on multiple machines, owned by different individuals, companies or organization. With federation protocols those instances can interact and form one network of many nodes (servers hosting similar services). One might be able to shut down one node but never the entire network. In such a setup censorship is practically impossible.

Think of how we use E-mail; you can choose any service provider or set up your own, and still exchange emails with people using another email provider. E-mail is built upon a decentralized and federated protocol."