A cold wave (known in some regions as a cold snap, cold spell, or Arctic Snap) is a weather phenomenon that is distinguished by a cooling of the air. Specifically, as used by the U.S. National Weather Service, a cold wave is a rapid fall in temperature within a 24-hour period requiring substantially increased protection to agriculture, industry, commerce, and social activities. The precise criteria for a cold wave are the rate at which the temperature falls and the minimum temperature to which it falls. This minimum temperature is dependent on the geographical region and time of year.

Source: Wikipedia