Graceful Degradation. Losing function in proportion to failure, with boundaries that contain damage — degrading in function, never in truth or safety; recovering deterministically.
A degraded system needs a named failure domain: the part allowed to lose function while unrelated work continues. It may use a governed fallback path, but the fallback must preserve the same truth and safety floor as the primary path. A circuit breaker is one way a system enters degraded operation deliberately instead of continuing to amplify a failing dependency.