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

  A family of secret-key cryptographic algorithms acting on input data of arbitrary length to produce an output value of a specified length (called the MAC of the input data). The MAC can be employed to provide an authentication of the origin of data and/or data-integrity protection. In this Recommendation, approved MAC algorithms are used to determine families of pseudorandom functions (indexed by the choice of key) that are employed during key derivation.
Sources:
NIST SP 800-108r1 [August 2022 (Includes updates as of 02-02-2024)] under message authentication code

  A family of symmetric-key cryptographic algorithms that act on input data of arbitrary length to produce an output value of a specified length (i.e., the MAC of the input data). The MAC can be employed to authenticate the origin of the input data and/or provide data integrity protection.
Sources:
NIST SP 800-227 under message authentication code

  A cryptographic checksum on data that uses a symmetric key to detect both accidental and intentional modifications of the data.
Sources:
NISTIR 7711 under Message Authentication Code