Implementations of formal AC policy such as AC model. Access control mechanisms can be designed to adhere to the properties of the model by machine implementation using protocols, architecture, or formal languages such as program code.
Sources:
NIST SP 800-192
under Access Control Mechanism
Security safeguards (i.e., hardware and software features, physical controls, operating procedures, management procedures, and various combinations of these) designed to detect and deny unauthorized access and permit authorized access to an information system.
Sources:
CNSSI 4009-2015
The logical component that serves to receive the access request from the subject, to decide, and to enforce the access decision.
Sources:
NIST SP 800-162