Supercritical water is a distinct thermodynamic state of water occurring above its critical temperature (374 °C) and critical pressure (22.1 MPa), where the liquid and gaseous phases are indistinguishable. As an academic concept and field of study, research into supercritical water investigates its unique physical and chemical properties, including variable density, viscosity, diffusivity, and dielectric constant, which govern its behavior as a tunable solvent and reaction medium. Its significance lies in its diverse applications, such as advanced power generation cycles (including Supercritical Water Reactors), waste treatment processes (like supercritical water oxidation), and chemical synthesis, leveraging its capacity to dissolve organic substances and facilitate reactions under extreme conditions.