System Security Plan — a document describing a system's boundaries, the controls it implements, and how each control is satisfied.
An SSP (System Security Plan) is the core artifact in NIST SP 800-53/800-171-based assessments (including FedRAMP and CMMC). It describes the system boundary, the environment, and — control by control — how the requirement is met, by whom, and with what evidence. Assessors evaluate the SSP against the actual environment.
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