Individual or organization having a right, share, claim, or interest in a system or in its possession of characteristics that meet their needs and expectations.
Sources:
NIST SP 800-160v1r1
from
ISO/IEC/IEEE 15288:2015
Individual, team, organization, or classes thereof, having an interest in a system.
Sources:
NIST SP 800-160v1r1
under stakeholder (system)