- a number representing the effect of temperature and humidity on humans by combining the two variables into an “apparent” temperature, introduced as a replacement for the temperature-humidity index: a temperature of 90° and relative humidity of 65 percent combine to produce a heat index of 102. Abbreviation: H.I.
- 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. Also called apparent temperature