From the National Weather Service glossary:
"Frost: The formation of ice crystals on the ground or other surfaces in the form of scales, needles, feathers, or fans. Frost develops under conditions similar to dew, except the temperatures of the Earth's surface and earthbound objects fall below 32oF. As with the term "freeze", this condition is primarily significant during the growing season. If a frost period is sufficiently severe to end the growing season or delay its beginning, it is commonly referred to as a "killing frost". Because frost is primarily an event that occurs as the result of radiational cooling, it frequently occurs with a temperature reading in the mid 30s."
"Frost/Freeze Advisory: This product is issued by the National Weather Service when freezing temperatures or conditions conducive to the formation of frost occur during the growing season.
Frost Point: Dew point below freezing."