A unit of thermodynamic temperature and a unit of the absolute temperature scale in which absolute zero corresponds to 0 kelvin. Originally, the kelvin was defined as 100/27.316 of the triple point of water (when the equilibrium of solid, liquid and gas phases occurs). The magnitude of one kelvin is the same as the magnitude of one degree Celsius. The melting point of ice at normal pressure corresponds to 273.15 kelvin and the boiling point of water at normal pressure corresponds to 373.15 kelvin. The kelvin is one of the SI units.