A hard frost is a term used to describe a weather condition where the temperature drops below freezing causing a thin layer of ice to form on objects. Other synonyms to describe this weather condition include killing frost, severe frost, black frost, and deep frost. A killing frost typically refers to a frost that is strong enough to damage or kill plants, while a severe frost denotes a lower temperature than a typical light frost. Black frost refers to a form of frost that is so severe it leaves crops blackened and damaged. A deep frost, on the other hand, refers to a colder and longer-lasting freeze, causing the ground to freeze deeper than usual.