A distillation of experience designing, implementing, integrating, and upgrading systems that systems engineers and architects can use to guide design decisions and analysis. A design principle typically takes the form of a terse statement or a phrase identifying a key concept, accompanied by one or more statements that describe how that concept applies to system design (where “system” is construed broadly to include operational processes and procedures, and may also include development and maintenance environments).
Sources:
NIST SP 800-160 Vol. 2 Rev. 1