Pressure exerted by the vapor phase is called the vapor pressure. Vapor pressure is a relative measure of the tendency to evaporate, depends on the nature of the substance and ambient temperature, and reaches a state of equilibrium (where no more vapors escape from the substance) in closed spaces.
Example: Water will boil at different temperatures at different pressure. The higher elevation (mountain and highlands) with lower pressure that water will boil at lower temperature than 100°C. Likewise, lower elevation at sea level will make water boil at approximately 100°C.