Subject Posted on December 20, 2019December 20, 2019 by Ty Mezquita Image Source A subject is an individual, process, or device causing information to flow among objects or a change to the system state; in other words, an active entity. Related Terms: Access, Access Control Source: NIST SP 800-53 Rev 4., CNSSI 4009 Share this on your social networks. Help Friends, Family, and Colleagues become more aware and secure.