Wind chill is the term referring to the apparent temperature felt by the skin in cold weather (as opposed to the actual temperature). Where T is the temperature in degrees Fahrenheit and V is the wind speed in miles per hour, the formula for calculating the wind chill is as follows: 35.74 + 0.6215 T - 35.75 V 0.16 + 0.4275 T V 0.16  This formula, based on calculations by IUPUI professor Maurice Bleustein, was adopted by the United States Weather Service and the Meteorological Services of Canada in 2001 to replace a formula that had been found to be less accurate. One of the changes that was made was that the temperature used was that five feet from the ground rather than 33 feet from the ground. 
The term was coined by Antarctic explorer Paul Siple in 1939. Note that the term "heat index" is used instead when the apparent temperature is hotter than the actual temperature, typically because of the effects of humidity.