A thin, wispy cloud found at high altitudes is a cirrus cloud.
Cirrus clouds are made primarily of ice crystals because they form high in the troposphere, where temperatures are well below freezing. Their delicate strands can look feathery, hair-like, or curled. They are usually white and often transparent enough for the Sun or Moon to shine through them.
The word “cirrus” comes from Latin for “curl” or “fringe.” Luke Howard included the term in his influential 1803 cloud-classification system, which helped establish the modern naming of cloud forms. The World Meteorological Organization recognizes cirrus as a cloud genus with several species, including fibratus, uncinus, floccus, castellanus, and spissatus.
Cirrus clouds generally produce no precipitation that reaches the ground. Ice crystals may fall from them as virga, but the crystals usually evaporate or sublimate in warmer, drier air below. A growing veil of cirrus can sometimes signal that a warm front or storm system is approaching. Cirrus should not be confused with flat stratus, towering cumulus, or thick rain-bearing nimbostratus.