AbstractFlow–Thermodynamics Theory extends classical thermodynamics by introducing the flow parameter S, which characterizes the dynamic state of the medium. Temperature, heat capacity, pressure, entropy, internal energy and phase behavior become S-dependent rather than fixed material properties. High-S environments amplify thermal transport, diffusion, radiative flux, sound speed and reaction activity, while low-S environments suppress thermal motion, stabilize structure and shift phase boundaries. The theory unifies gases, liquids, solids, plasmas and extreme astrophysical media under a single scaling framework, showing that thermodynamic quantities scale linearly or logarithmically with S. New flow-driven phases (S-solids, S-liquids, S-plasmas, S-exotic) and hybrid transition states emerge when S crosses critical thresholds. By replacing static equations with S-scaled relations (T·S, C·S, PV=nRTS, q∝S∇T, S_entropy∝ln(Ω·S)), Flow–Thermodynamics reveals that matter does not define thermodynamics; flow defines matter. This framework links thermodynamics with flow physics, relativity, quantum behavior and cosmology, providing a unified description from planetary interiors to stellar atmospheres and relativistic jets.