We propose a semi-classical framework, PostulateQ, that offers a microscopic, geometric interpretation of what mass is — not how it behaves, which established physics already describes with precision. The central claim is ontological: mass is not a fundamental substance but the name for null energy (an electromagnetic wave) closed upon itself into a persistent, self-balanced loop. Radiation and matter become two topologies — open and closed — of the same conserved energy, connected by a single continuous accrual rule. PostulateQ does not reconstruct General Relativity from first principles, nor replace it. GR is taken as given: the framework interprets what curves spacetime microscopically, as statistical mechanics interprets thermodynamics without replacing it. Within this reading, gravitation appears in two roles — direct (energy curving spacetime, as in GR) and converse (a null path acquiring curvature from the geometry it produces), whose fixed point is a stable closed configuration, in the spirit of Wheeler's geon. The framework introduces no new empirical predictions; every result reproduces established physics. Its contribution is a change of perspective: with mass appearing only as a derived label rather than a primitive, the boundary between light and matter becomes a continuous coordinate rather than a categorical divide. We set out the construction, its verified consistencies, and — with equal care — the open problems it does not resolve, offering the reader a different vantage point from which to view the nature of matter.