An access control policy that is uniformly enforced across all subjects and objects within the boundary of an information system. A subject that has been granted access to information is constrained from doing any of the following: (i) passing the information to unauthorized subjects or objects; (ii) granting its privileges to other subjects; (iii) changing one or more security attributes on subjects, objects, the information system, or system components; (iv) choosing the security attributes to be associated with newly-created or modified objects; or (v) changing the rules governing access control. Organization-defined subjects may explicitly be granted organization-defined privileges (i.e., they are trusted subjects) such that they are not limited by some or all of the above constraints.
Sources:
CNSSI 4009-2015 under mandatory access control (MAC)

  See mandatory access control (MAC).
Sources:
CNSSI 4009-2015

  A means of restricting access to system resources based on the sensitivity (as represented by a label) of the information contained in the system resource and the formal authorization (i.e., clearance) of users to access information of such sensitivity.
Sources:
NIST SP 800-44 Version 2 under Mandatory Access Control

  See Mandatory Access Control.
Sources:
NIST SP 800-53 Rev. 5 under nondiscretionary access control