Covering of ice caused by locally sub-freezing temperatures.
Frost is formed when water vapour freezes and forms an ice covering over the ground and/or plants. Typically frost forms when the air temperature drops below freezing (0C, 32F) - this is an air frost.
Moisture evaporation can cause localized drops in air temperature close to the ground. This results in a ground frost where frost is formed even though the air temperature a few feet above the ground remains just above freezing.
Frosts can damage plants, crops, and fruit. Use this tag for questions about hardiness against frosts, and how to protect sensitive plants against frosts.