Source : WordNet®

supercomputer
     n : a mainframe computer that is one of the most powerful
         available at a given time

Source : Free On-Line Dictionary of Computing

supercomputer
     
         A broad term for one of the fastest computers
        currently available.  Such computers are typically used for
        {number crunching} including scientific {simulations},
        (animated) {graphics}, analysis of geological data (e.g. in
        petrochemical prospecting), structural analysis, computational
        fluid dynamics, physics, chemistry, electronic design, nuclear
        energy research and meteorology.  Perhaps the best known
        supercomputer manufacturer is {Cray Research}.
     
        A less serious definition, reported from about 1990 at The
        {University Of New South Wales} states that a supercomputer is
        any computer that can outperform {IBM}'s current fastest, thus
        making it impossible for IBM to ever produce a supercomputer.
     
        (1996-12-13)