Source : Free On-Line Dictionary of Computing

attoparsec
     
         About 31 mm (one inch).  "atto-" is the
        standard {SI} {prefix} for multiplication by 10^-18.  A parsec
        (parallax-second) is 3.26 light-years; an attoparsec is thus
        3.26 * 10^-18 light years.  Thus, one attoparsec per
        {microfortnight} is about one inch per second.
     
        This unit is reported to be in use (though probably not very
        seriously) among hackers in the UK.
     
        [{Jargon File}]
     
        (1996-12-08)