Humidity is the concentration of water vapor present in the air. Water vapor, the gaseous state of water, is generally invisible to the human eye. Humidity indicates the likelihood for precipitation, dew, or fog to be present. Humidity depends on the temperature and pressure of the system of interest. ...

The relative humidity {\displaystyle (RH}{\displaystyle (RH} or {\displaystyle \phi )}{\displaystyle \phi )} of an air-water mixture is defined as the ratio of the partial pressure of water vapor {\displaystyle (p_{H_{2}O})}{\displaystyle (p_{H_{2}O})} in the mixture to the equilibrium vapor pressure ...