ground frost

Noun

• The condition of air temperature dropping below the freezing point at or near ground level.
• Ice produced by the direct deposition of water vapor on grass, trees and other objects in freezing conditions.
• The frozen upper level of soil, caused by the air temperature dropping below the freezing point for a lengthy period of time; in temperate climates the soil thaws completely for the summer and in cold climates it may develop to permafrost.