biff /bif/ vt.
To notify someone of incoming mail. From
the BSD utility
biff(1), which was in turn named after a
friendly dog who used to chase frisbees in the halls at
UCB while 4.2BSD was in development. There was a legend that it
had a habit of barking whenever the mailman came, but the author of
biff says this is not true. No relation to B1FF.