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