Supercritical “steam” is supercritical water because, at supercritical pressures, fluid is considered a single-phase substance. However, this term is widely (and incorrectly) used in the literature in relation to supercritical “steam” generators and turbines.
See also: Supercritical Water
At pressure that is higher than the critical pressure, water is in a special state, which is known as the supercritical fluid state. A supercritical fluid is a fluid that is at pressures higher than its thermodynamic critical values. At the critical and supercritical pressures, a fluid is considered a single-phase substance, although all thermophysical properties undergo significant changes within the critical and pseudocritical regions.
See also: Critical Point of Water