The right or a permission that is granted to a system entity to access a system resource.
Sources:
NIST SP 1800-10B under Authorization from NIST SP 800-82 Rev. 2
NIST SP 1800-27C under Authorization from NIST SP 800-82 Rev. 2
NIST SP 800-82 Rev. 2 under Authorization from RFC 4949

  Access privileges granted to a user, program, or process or the act of granting those privileges.
Sources:
CNSSI 4009-2015
NIST SP 800-160 Vol. 2 Rev. 1 from CNSSI 4009-2015
NIST SP 800-53 Rev. 5 from CNSSI 4009-2015
NIST SP 800-53A Rev. 5 from CNSSI 4009-2015

  The official management decision given by a senior official to authorize operation of a system or the common controls inherited by designated organizations systems and to explicitly accept the risk to organizational operations (including mission, functions, image, and reputation), organizational assets, individuals, other organizations, and the Nation based on the implementation of an agreed-upon set of security and privacy controls. Also known as authorization to operate.
Sources:
NIST SP 800-12 Rev. 1 under Authorization

  The process of verifying that a requested action or service is approved for a specific entity.
Sources:
NIST SP 800-152 under Authorization
NIST SP 800-57 Part 2 Rev.1 under Authorization

  See Accreditation.
Sources:
NIST SP 800-18 Rev. 1 under Authorize Processing

  Access privileges granted to an entity; conveys an “official” sanction to perform a cryptographic function or other sensitive activity.
Sources:
NIST SP 800-57 Part 2 Rev.1 under Authorization

  See authorization.
Sources:
CNSSI 4009-2015 under authorize processing
NIST SP 800-137 under Security Authorization

  Access privileges that are granted to an entity that convey an “official” sanction to perform a security function or activity.
Sources:
NIST SP 800-57 Part 1 Rev. 5 under Authorization

  The process of granting or denying specific requests for obtaining and using information and related information processing services; and to enter specific physical facilities (e.g., Federal buildings, military establishments, and border crossing entrances).
Sources:
NIST SP 800-53 Rev. 5 under access control

  The decision to permit or deny a subject access to system objects (network, data, application, service, etc.)
Sources:
NIST SP 800-162 under access control

  The official management decision of the Designated Authorizing Official to permit operation of an issuer after determining that the issuer’s reliability has satisfactorily been established through appropriate assessment processes.
Sources:
NIST SP 800-79-2 under Authorization

  The granting or denying of access rights to a user, program, or process.
Sources:
NISTIR 7316 under Authorization

  The process of initially establishing access privileges of an individual and subse­quently verifying the acceptability of a request for access.
Sources:
NISTIR 4734 under Authorization