This paper continues the geometric-informational interpretation of relativity, in which proper time is understood as the rhythm of physical processes. The central theme is the nature of mass. Relativistically, invariant mass is not a separate substance, but the total energy of a system in its centre-of-momentum frame divided by c². For stable or quasi-stable physical objects, this total energy is embodied in an organized physical configuration: fields, internal motion, binding, stresses, and phase evolution. The paper argues that this provides a natural bridge from mass to intrinsic rhythm, from intrinsic rhythm to proper time, and from energy-momentum to metric response. It distinguishes between the invariant mass of an arbitrary relativistic system, the rest mass of stable objects, the Higgs contribution, QCD contributions, binding energy with either sign, the role of internal stresses, and the de Broglie-Compton link between mass and an intrinsic scale of rhythm/phase. The quantitative element is the Compton link: mass defines the Compton frequency fC = mc²/h, and the associated phase accumulates along proper time, so that gravitational time dilation can be read as a difference in the accumulation of intrinsic phase between systems in different metric regions. This work continues the program of the companion preprint (DOI: 10. 5281/zenodo. 20665730).
Olivian Barbu (Fri,) studied this question.