Subcritical water is water heated under pressure to a temperature between its normal boiling point (100°C) and its critical point (374°C), maintaining it in the liquid state. Under these conditions, its physicochemical properties, such as dielectric constant, viscosity, and ion product, are significantly altered compared to ambient water. As an academic concept and methodological approach, research investigates subcritical water's unique properties as a versatile and environmentally benign reaction medium and solvent for applications including chemical synthesis, extraction, and the degradation of organic and inorganic materials.