A pair of  of Dew point pressure (P_d) and Dew point temperature (T_d) at which the phase transition between liquids and gaseous states of the matter ( condensation / vaporization ) starts happening.

See also

Petroleum Industry / Upstream / Subsurface E&P Disciplines / Fluid Analysis (PVT) / Dynamic fluid properties

[ Dew point pressure (P_d) ][ Dew point temperature (T_d) ]