This paper proposes a formal physical definition of memory based on complex spacetime and closed-surface pattern theory.Using the representation Z=X+ict, the real axis corresponds to irreversible physical space, while the imaginary axis represents a reversible internal dimension where pattern states evolve.The physical memory of a closed surface is defined as the integrated pattern history: M=∫P(t) dt. When these accumulated patterns become fixed on the real axis, they appear as material memory, spatial curvature, stress fields, or cosmological structure.This framework unifies material memory, spatial memory, biological memory, observation-induced memory, and cosmic pattern retention under a single geometric ontology.The paper establishes memory as a fundamental physical quantity arising from closed-surface dynamics.