Villi are projections of a biological tissue that look hairy in appearance.
They are found for example in the intestines and in the placenta.
They increase the exchange surface area between two media. For example, absorption of nutrients in the small intestine is facilitated.
They must not be confused with microvilli which are folds in the membrane of an epithelial cell.
The intestinal villi, which are parallel and vertical, are seen between the light (white, above) and different cell layers of the intestinal wall. DR Credits.