The part of the OT system used to monitor and control the physical process. This includes all control servers, field devices, actuators, sensors, and their supporting communication systems.
Sources:
NIST SP 800-82r3 under Control

  See security control and privacy control.
Sources:
NIST SP 800-37 Rev. 2

  See security control or privacy control.
Sources:
NIST SP 800-53 Rev. 5
NIST SP 800-53A Rev. 5

  A measure that is modifying risk. (Note: controls include any process, policy, device, practice, or other actions that modify risk.)
Sources:
NIST SP 1800-15B under Control from NISTIR 8053
NIST SP 1800-15C under Control from NISTIR 8053

  The means of managing risk, including policies, procedures, guidelines, practices, or organizational structures, which can be of an administrative, technical, management, or legal nature.
Sources:
NIST SP 800-160 Vol. 2 Rev. 1 from ISACA Glossary of Terms

  Purposeful action on or within a process to meet specified objectives.
Sources:
NIST SP 800-160v1r1

  The mechanism that achieves the action.
Sources:
NIST SP 800-160v1r1

  Measure that is modifying risk.
Sources:
NIST SP 800-188

  measure that is modifying risk. (Note: controls include any process, policy, device, practice, or other actions which modify risk.)
Sources:
NISTIR 8053