Systems security engineering is a specialty engineering field strongly related to systems engineering. It applies scientific, engineering, and information assurance principles to deliver trustworthy systems that satisfy stakeholder requirements within their established risk tolerance. See also information systems security engineering (ISSE).
Sources:
CNSSI 4009-2015

  Process that captures and refines security requirements and ensures their integration into information technology component products and information systems through purposeful security design or configuration.
Sources:
NIST SP 800-37 Rev. 2

  A specialty engineering field strongly related to systems engineering. It applies scientific, engineering, and information assurance principles to deliver trustworthy systems that satisfy stakeholder requirements within their established risk tolerance.
Sources:
NIST SP 800-53 Rev. 5

  A transdisciplinary and integrative approach to enable the successful secure realization, use, and retirement of engineered systems using systems, security, and other principles and concepts, as well as scientific, technological, and management methods. Systems security engineering is a subdiscipline of systems engineering.
Sources:
NIST SP 800-160v1r1