Aggers and all. There was a time when your browser would throw an error code, but not much else: 400 Bad file request; 404 File not found; 408 Request timeout; 500 Internal server error, and so on.
They were meaningless to most people so newer browsers give a bit more information:
See this Unfortunately some of the explanations look a bit dodgy or almost as confusing as the old error codes! Best bet is to close the tab and try again, and if it does not work, give up - as Homer would say.