This article is from the Computer Security Evaluation FAQ, by Trusted Product Evaluation Program TPEP@dockmaster.ncsc.mil.
A division is a set of classes (see Question 5) from the
Trusted Computer System Evaluation Criteria (TCSEC) (see
Section II, Question 1). There are 4 divisions A, B, C, and D
in decreasing order of assurance and features. Thus, a system
evaluated at a class in division B has more security features
and/or a higher confidence that the features work as intended
than a system evaluated at a class in division C. Although the
Computer Security Subsystem Interpretation (CSSI) of the TCSEC
specifies criteria for various D ratings, these are not
reflected in the TCSEC itself, which has no requirements for D
division systems. An unrated system is, by default, division
D.
 
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