What does the term 'Cirrus' refer to in cloud classification?

The term 'Cirrus' refers to a specific classification of clouds that are characterized by their high altitude and thin, wispy appearance. These clouds typically form at altitudes above 20,000 feet (approximately 6,000 meters) in the atmosphere and are composed primarily of ice crystals due to the low temperatures found at those heights.

Cirrus clouds are often indicators of fair weather but can also signify that a change in the weather is on the way, particularly if they begin to thicken and develop into different cloud types. Their high altitude sets them apart from low and middle altitude clouds, which are categorized differently based on their formation height and characteristics. This classification is important in meteorology for predicting weather patterns and understanding atmospheric conditions. Thus, recognizing cirrus as high altitude clouds is essential in fields related to aviation and weather forecasting.