“This is Paper 1 of an 8-part series, with subsequent papers released weekly.” This paper proposes the regular tetrahedron as a fundamental quantum of volume suitable for discrete geometric models of spacetime. Rather than treating spacetime as a smooth continuum, the work explores how a tetrahedral unit can function as the minimal volumetric building block within a tessellating lattice, preserving both topological consistency and volumetric balance. The tetrahedron is examined not merely as a geometric primitive, but as an information-bearing unit whose combinatorial structure enables exact space-filling when paired with its dual octahedral regions. Emphasis is placed on the tetrahedron’s uniquely low degree of freedom, its role in defining minimal spatial volume, and its capacity to support deformation while preserving global topology. These properties suggest a robustness that may be relevant under quantum-scale fluctuations or “geometric jitter.” By framing the tetrahedron as a quantum of volume rather than a mere element of classical geometry, this paper establishes a foundation for subsequent investigations into discrete spacetime scaffolds, informational geometry, and low-degree-of-freedom lattice models. The work is intended as a conceptual and geometric contribution, offering a fresh perspective on how fundamental spatial structure might arise from simple, stable units. “Version 3 corrects the cover-page year to 2026.”