(1) The force exerted by a vapor. If a vapor is kept in confinement over its liquid so that it can accumulate above the liquid, the temperature being held constant, the vapor pressure approaches a fixed limit called the maximum or saturated vapor pressure, dependant only on the temperature and the liquid. The term vapor pressure is sometimes used as synonymous with saturated vapor pressure. (2) Force, usually expressed in millimeters of mercury or pascals, at any given temperature of a vapor in equilibrium with its liquid or solid form.
