Vapor pressure is the pressure exerted by a vapor in equilibrium with its liquid or solid form at a given temperature. It indicates how readily a substance evaporates; higher vapor pressure means a substance evaporates more easily. For example, water has a higher vapor pressure at higher temperatures, which is why it evaporates faster when heated. The vapor pressure of a substance is influenced by temperature and the nature of the substance itself. Each liquid has a specific vapor pressure at a given temperature, which can be measured in units like atmospheres or millimeters of mercury. Understanding vapor pressure is important in fields like chemistry and meteorology.