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A system that provides support to the life cycle activities associated with the system of interest. Enabling systems are not necessarily delivered with the system of interest and do not necessarily exist in the operational environment of the system of interest.
NIST SP 800-160 Vol. 2 Rev. 1 from ISO/IEC/IEEE 15288:2015
System that supports a system of interest during its life cycle stages but does not necessarily contribute directly to its function during operation.
NIST SP 800-160v1r1 from ISO/IEC/IEEE 15288:2015