TBI, this is what is being referred to. At the time I grabbed this screenshot there was no-one logged in as Anonymous, but sometimes that number can be as high as 4 or 5. It's different to being logged in as a Guest which is just someone who hasn't bothered to log in (could be a member, or just a passer-by who has never registered). Anonymous can only be a registered member, and is a conscious decision for whatever reason.