@davoloid @inexcode
How isolated an instance is from the others. Which means how much the people from one instance stay together.
It's the amount of mentions of users from other instances divided by the total amount of mentions.

This provides no information regarding how wide the network of the instance is, since you might have a very low insularity with just one federated instance. This might be the case of a small instance in a very specific field which often addresses users from the same field in a larger instance.