A measurement of the air temperature that factors in the effect of relative humidity, used as an indicator of the perceived temperature.
A number expressed in degrees Fahrenheit, computed from the temperature and the relative humidity, and used as an indication of the apparent temperature as it would be felt by a person outdoors (Ex.: a temperature of 90°F and a relative humidity of 50% yield a heat index of 96°F)
A measurement of the air temperature in relation to the relative humidity, used as an indicator of discomfort. The heat index is higher when high air temperatures occur with high humidity, and lower when they occur with low humidity. The heat index is based on studies of skin cooling caused by the evaporation of sweat.