The pressure of a vapor in equilibrium with its condensed phase (liquid or solid). This equilibrium is dynamic in that evaporation and condensation are both occurring but are in equilibrium. It is a function of temperature only and is nearly independent of the existence or density of other gases in a system. It may, however, be dependent on the shape of the surface of the condensed phase. More generally, the equilibrium vapor pressure with respect to small droplets containing soluble impurities may be quite different from the saturation vapor pressure.