1. (properly, capitalized) One of the line of supercomputers designed by Cray Research.
2. Any supercomputer at all.
3. The canonical number-crunching
The term is actually the lowercased last name of Seymour Cray, a noted computer architect and co-founder of the company. Numerous vivid legends surround him, some true and some admittedly invented by Cray Research brass to shape their corporate culture and image.