Mandatory Access Control (MAC)

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.
SOURCE: SP 800-44

Access controls (which) are driven by the results of a comparison between the user’s trust level or clearance and the sensitivity designation of the information.
SOURCE: FIPS 191

A means of restricting access to objects based on the sensitivity (as represented by a security label) of the information contained in the objects and the formal authorization (i.e., clearance, formal access approvals, and need-to-know) of subjects to access information of such sensitivity. SOURCE: CNSSI-4009