A standard from the U.S. National Computer Security Council (an arm of the National Security Agency). It defines criteria for trusted computer products and describes four trust levels, designated as A, B, C, and D. Each level of trust includes more features and requirements: Farlex, Inc. The Orange Book. [Online, 2004.] Farlex, Inc. Website. http://computing-dictionary.thefreedictionary.com/Orange%20Book.