Definition of red box:
(n) :
(UK politics) A secure briefcase-like box used by ministers in the British government to carry their documents.
(n) :
(US, military) A safe located at a nuclear installation containing launch codes.
(n) :
(informal, US, meteorology) A "tornado watch" notification, indicating that conditions might lead to a tornado though none has yet been sighted.
(n) :
A phreaking device that generates tones to simulate the insertion of coins into a payphone, thus enabling the user to make illegitimate free calls.