A villus (pl. villi) is a thin, finger-like epithelial projection made from simple columnar epithelial tissues. It lines several animal organs such as the small intestine, the fetal chorion, and the arachnoid membrane of the human brain.
The term villus is derived from a Latin word which refers to a thick tuft of hair that is comparable to fleece.
The villi are an evolved trait used to extend the surface area of the organβs cellular lining. In organs such as the small intestine, the additional surface area is used to increase the space and ability of transport proteins to absorb nutrients through the intestinal wall. A similar process occurs in the microvilli, hence the similar name.