Complex sentence: Relative humidity is the amount of water vapor in a mixture of air and water vapor; specifically, it is the ratio of the partial pressure of water vapor in the air-water mixture to the saturated vapor pressure of water at the prescribed temperature.
Split into simpler sentences: Relative humidity is a term used to describe the amount of water vapor in a mixture of air and water vapor. It is defined as the ratio of the partial pressure of water vapor in the air-water mixture to the saturated vapor pressure of water at the prescribed temperature.