Saturation point

From Glossary of Meteorology

saturation point

A point on a thermodynamic diagram representing the state of the air defined by a pair of variables: Psat and Tsat, where Psat is the saturation pressure and Tsat is the saturation temperature.

These latter variables are the pressure and temperature of an air parcel that was raised dry- adiabatically or lowered moist-adiabatically until it was just at saturation. The saturation point is a conserved variable for adiabatic motion and thus serves as a tracer for the air parcel on a thermodynamic diagram.