What is the term for the ratio between the actual pressure of a vapor to its saturation pressure in the atmosphere?

The term that describes the ratio between the actual pressure of a vapor to its saturation pressure in the atmosphere is relative humidity. Relative humidity is expressed as a percentage and indicates how much moisture the air contains compared to the maximum amount of moisture it can hold at a given temperature.

In essence, if the relative humidity is 100%, the air is fully saturated with water vapor and cannot hold any more moisture without the vapor condensing into liquid. If the relative humidity is lower than 100%, it indicates that the air can still absorb more moisture, which is crucial for understanding weather patterns and conditions.

The other terms listed do not pertain to this specific concept. For instance, absolute pressure refers to the total pressure exerted by a gas without any reference to surrounding atmospheric pressure. The dew point is the temperature at which the air becomes saturated and moisture begins to condense, and partial pressure describes the pressure that a single component of a mixture of gases would exert if it occupied the same volume alone.