Here's why:

* Cirrus comes from the Latin word for "curl" or "lock of hair," which accurately describes their wispy, feathery appearance.

* They are found in the highest layer of the atmosphere, the tropopause and the stratosphere, at altitudes above 20,000 feet (6,000 meters).

There are other types of high altitude clouds, but they are all categorized as cirrus:

* Cirrostratus: Thin, sheet-like clouds that often cover the entire sky.

* Cirrocumulus: Small, white puffs of clouds arranged in rows.

* Cirrocumulus lenticularis: Lenticular (lens-shaped) clouds that form over mountains.

* Cirrus uncinus: Hook-shaped clouds that are often a sign of approaching bad weather.

Let me know if you'd like to learn more about any specific type of cirrus cloud!