A skeuomorph, or skeuomorphism (Greek: skeuos—vessel or tool, morphe—shape), is a derivative object that retains ornamental design cues to a structure that was necessary in the original. Skeuomorphs may be deliberately employed to make the new look comfortably old and familiar, such as copper cladding on zinc pennies or computer printed postage with circular town name and cancellation lines. An alternative definition is “an element of design or structure that serves little or no purpose in the artifact fashioned from the new material but was essential to the object made from the original material”. This definition is narrower in scope and ties skeuomorphs to changes in materials.
Skeuomorph (including examples of both physical and digital skeuomorphs) on Wikipedia.