Wool is the fiber derived from the hair of some animals, usually sheep. It has two qualities that distinguish it from hair or fur: it is scaled in such a way that helps the animal move out burrs and seeds that might embed themselves into its skin; and it is crimped, in some fleeces more than 20 bends for every few centimeters.
It is possible to spin and felt the fleece. They help the individual fibers "grab" each other so that they stay together. They also make the product retain heat, as they trap heat in their bends.
Wool is processed into clothing, carpeting, felt, thread, and padding. Wool was also used to make sails and tents. As the raw material has been readily available since the widespread domestication of sheep and similar animals, the use of wool for clothing and other fabrics dates back to some of the earliest civilizations. Wool against bare skin can be very itchy (causing some people to mistakenly believe that they are alergic to the cloth), and it often found in history with either an lining of linen or a second undergarment of linen. The further down the social spectrum and the earlier the time period, the less likely this is to occur.
Wool takes dye easily and the natural oils found in sheep's wool make such cloth quite water resistant. Even with the lanolin removed, wool sheds water easiliy and remains warm when wet as well as being an excellent insulator when dry. People who make cloaks and clothing from cotton rather than wool can usually be identified as the ones closest to the fire trying to keep warm.
In the middle ages, wool that was combed was described as 'cottoned'.