What is defined as the pressure exerted by a vapor in equilibrium with its liquid or solid phase?

The pressure exerted by a vapor in equilibrium with its liquid or solid phase is known as vapor pressure. This concept is important in understanding how substances behave under different temperature and pressure conditions. Vapor pressure reflects the tendency of a substance to evaporate or sublimate, which is crucial in various applications, including weather forecasting, safety assessments in hazmat situations, and understanding material properties in chemistry.

In contrast, boiling point refers to the temperature at which a liquid's vapor pressure equals the surrounding atmospheric pressure, leading to the formation of vapor bubbles within the liquid. Atmospheric pressure is the force exerted by the weight of the air above a surface and is not directly related to the specific properties of a liquid or solid's vapor. Relative humidity indicates the amount of water vapor present in the air compared to the maximum amount of water vapor the air can hold at a given temperature, but does not directly address the equilibrium state of vapor with liquid or solid phases. Thus, vapor pressure directly encapsulates the equilibrium dynamic described in the question.