Corn and calluses are thick, hard layers of dead skin that usually form under the feet, at the sides of the toes or above the toes.
A callus is a more diffused thickening of the skin whereas a corn is a thicker and more focused. A corn is often cone shaped, and can extend deep into the skin. It may also be surrounded by callus.
Corns are usually hard, but those that occur between the toes may be kept soft by moisture in the area.
People who play stringed muscial instruments like the guitar and violin may also have calluses forming on their fingers, and, in the case of violinists, at the neck where the violin is placed. Likewise, farmers and rowers tend to have corn and calluses on their hands.