blue box

n.

1. obs. Once upon a time, before all-digital switches made it possible for the phone companies to move them out of band, one could actually hear the switching tones used to route long-distance calls. Early phreakers built devices called blue boxes that could reproduce these tones, which could be used to commandeer portions of the phone network. (This was not as hard as it may sound; one early phreak acquired the sobriquet "Captain Crunch" after he proved that he could generate switching tones with a plastic whistle pulled out of a box of Captain Crunch cereal!) There were other colors of box with more specialized phreaking uses; red boxes, black boxes, silver boxes, etc. There were boxes of other colors as well, but the blue box was the original and archetype.

2. n. An IBM machine, especially a large (non-PC) one.