Callus

A callus is an area of thick skin that forms due to pressure, friction or irritation. Repeated contact is needed for them to form. Calluses are often found on one's feet because of walking and badly fitting shoes. Though they may appear unsightly, calluses are not usually harmful. They can, however, lead to or cause other problems if neglected.
Calluses can also form on human hands. In particular, the middle, ring and index fingers are prone to calluses.
Construction work, having high heels on too much, rock climbing and playing musical instruments can cause calluses on the hands or feet. Certain sports can also cause calluses.