/är-inj bu̇k/
n. The U.S. Government's standards document 'Trusted Computer System Evaluation Criteria, DOD standard 5200.28-STD, December, 1985' which characterize secure computing architectures and defines levels A1 (most secure) through D (least). Stock UNIXes are roughly C2, and can be upgraded to about C1 without excessive pain.
See also book titles.