Wind chill is a calculation of the adjusted temperature because of air temperature and wind speed.
The colder the wind chill, the higher the chance of frostbite with less exposure time. See attached chart for the wind chill factor. Frostbite is really the combination of wind and cold temperatures attacking less than adequately protected skin. This can happen if one is stranded in the bitter cold, or if its cold enough, it can occur just crossing the street. The areas most likely to get frostbitten are ears, noses, fingers and toes.