Having the nature of a Cthulhu, the horrific tentacled green monstrosity from H.P. Lovecraft's seminal horror fiction. Cthulhu sends dreams that drive men mad, feeds on the flesh of screaming victims rent limb from limb, and is served by a cult of degenerates. Hackers think this describes large proprietary systems such as traditional mainframes, installations of SAP and Oracle, or rooms full of Windows servers remarkably well, and the adjective is used casually. Compare Shub-Internet and crawling horror.