In networked software, to be federated means users are able to send messages from one independent deployment to the other. In WordPress, this is achieved using linkbacks and feeds. So how would you define federation?

RSS can be considered a federated protocol, maybe...if you stretch the definition.

With RSS, you can subscribe to feeds with any standard reader. Interestingly enough, YouTube channels all have RSS feeds, so you can subscribe to them without needing to do so via a Google account.