So you need to look at the number of de federations. That is basically how many other instances have blocked them and do not receive content from them to their feed. You can still go to all these instances using their respective urls and see what they are like. The reasons for blocking them vary depending on the instance.
Edit:
They can still be federated with other instances that don't block them creating their own little fediverse bubbles.
Ok ok... So me using Lemmy.world is a specific instance of Lemmy, so it's almost like its own server? And other instances (maybe lemmy.unitiedstates?) is its own federated instance likely related to just U.S. posts and it can communicate with other instances? Do de-federated instances have no other communication with instances?
Apologies if these are silly, I feel like a dum dum because everyone else seems to grasp this except me.
You pretty much got it! One nitpick, your example of Lemmy.unitedStates is not NECESSARILY a federated instance, just an instance. It may or may not be federated with other instances.
De-federated instances lose communication to/from the instances that said "im gonna de-federate from these Nazis", so again you pretty much got it right :) not silly questions at all! It's a new concept to many people and I promise you MANY people have and will ask these "dumb" (but not actually) questions!
Defederated means that the server has been forbidden from connecting and communicating with specific other servers that have decided to defederate with it, so users from the server can't see or interact with users and posts on the server that defederated it and vice versa. Hopefully I was clear and coincise.