A corn (or clavus, plural clavi) is a specially shaped callus of dead skin that usually occurs on thin or glabrous (hairless and smooth) skin surfaces, especially on the dorsalsurface of toes or fingers.Corns and calluses are annoying and sometimes painful thickenings that form in the skin in areas of excessive pressure They can sometimes occur on the thicker palmar or plantar skin surfaces.

Corns form when the pressure point against the skin traces an elliptical or semi-elliptical path during the rubbing motion, the center of which is at the point of pressure, gradually widening. If there is constant stimulation of the tissue producing the corns, even after the corn is surgically removed, the skin may continue to grow as a corn. If the source of any abnormal pressure is detected, this may be avoided, such as with orthotics and conservative footwear with extra toe space.If no other treatment is effective, surgery must be performed.