What is the definition or description of: callus?

Toughened Skin: A callus is an area of skin that has become toughened, thick, and hard as a result of repeated pressure, friction or other irritation. Most commonly found on the feet due to walking. Generally calluses are not harmful. Calluses can also form on the fingers due to use of writing utensils, musical instruments, or even rock climbing. They are formed by keratinocytes in the outer layer of skin.