mission function

A category label for the primary, substantive activities that an organization exists to perform — its core business or operational work — as distinguished from the administrative, technical, and infrastructure activities (support functions) that exist only to enable or sustain that core work. In NIST SP 800-53 (AC-5) and its derivative publications, the contrast appears directly in the Separation of Duties control, which calls for "dividing mission functions and information system support functions among different individuals and/or roles." The practical import is that personnel who carry out an organization's primary operational work should be kept organizationally and functionally distinct from those who perform system support roles such as quality assurance, configuration management, network security, system management, assessments, and programming. The phrase is compositional — "mission" is a plain modifier meaning the organization's purpose or core business, and "function" carries its ordinary meaning — and no authority document assigns it a standalone technical definition distinct from that plain reading.