I think when many people say decentralised they mean federated, or something along those lines. Email and IRC today are, as far as I know, highly centralised,

I think when many people say decentralised they mean federated, or something along those lines. Email and IRC today are, as far as I know, highly centralised, but not in the same way that, say, social networks are. Even the web is somewhat centralised (and I suppose always has been, to some degree) but it's clearly and successfully federated.