A degree of frost is a non-standard unit of measure for air temperature equal to one degree Fahrenheit below the temperature at which water freezes (32 degrees Fahrenheit or 0 degrees Celsius).
A degree of frost is a non-standard unit of measure for air temperature meaning degrees below freezing point. In the US, it is equal to one degree Fahrenheit below the temperature at which water freezes (32 degrees Fahrenheit or 0 degrees Celsius).