The practice of building software around a precise, explicit representation of the real-world concepts in a business — users, accounts, feedback items, roadmap states — before writing feature code. Popularized by Eric Evans in Domain-Driven Design, it's the discipline that distinguishes products that age well from ones that collapse under their own special cases. For FeatureOS, domain modeling is why a well-shaped Feedback → Initiative → Release spine is more valuable than any single feature built on top of it.