Third perimeter: concept ownership in AI understanding. Build through: DefinedTermSet publication with termCodes, systematic term usage in content, tier-1/2 corroboration of concept ownership, OG-RAG compatible ontology. Test with concept queries (“What is [your term]?”). Target: your definition cited as authoritative. Most defensible perimeter — concepts require model retraining to displace. Enables category creation and pricing power. Requires domain sovereignty first (legitimacy prerequisite). Measure through vocabulary attribution testing. Most organizations are Undefended here.