1) Dryness fraction is defined as the ratio of the mass of actual dry steam to the mass of steam containing it.
2) Critical point a point on a phase diagram at which two phases of a substance have the same density, and are therefore indistinguishable.
3) Triple Point is the temperature and pressure at which solid, liquid, and vapor phases of a particular substance coexist in equilibrium.
4) Degree of superheat is the numerical amount by which the temperature of a superheated vapour exceeds the saturation temperature at the same pressure.