The universal argument is a concept copied from Emacs. It is provided by the prefix key C-u, and it typically causes the following command to behave in some special way --- whatever makes most sense for the particular command. With some commands, it can be doubled or tripled up for additional alternative actions. For example, supplying universal argument to the find-url command means find-url-in-new-buffer; supplying it twice means find-url-in-new-window. Supplying universal argument to the reload command causes reload to bypass the cache.