Quiz: Remember the definition of mal de mer?
pressure exerted by a vapour when the vapour is in equilibrium with the liquid or solid form, or both, of the same substance-i.e., when conditions are such that the substance can exist in both or in all three phases. Vapour pressure is a measure of the tendency of a material to change into the gaseous or vapour state, and it increases with temperature. The temperature at which the vapour pressure at the surface of a liquid becomes equal to the pressure exerted by the surroundings is called the boiling point (q.v.) of the liquid