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.