Cold air is defined as air that has a lower temperature compared to its surroundings. It is denser than warm air, which causes it to sink. This density difference plays a crucial role in weather patterns and can lead to the formation of clouds and precipitation. When cold air moves into an area, it can create a drop in temperature, often leading to chilly weather conditions. Cold air masses, such as those from the polar regions, can influence local climates and are often associated with cold fronts that bring changes in weather, including snow and frost.