A skeuomorph icon , or skeuomorphism (—vessel or tool, —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.

Physical skeuomorphs

Historically, high-status items, such as metal tableware, were often recreated for the mass market using ceramics, which were a cheaper material. In certain cases, efforts were made to recreate the rivets in the metal originals by adding pellets of clay to the pottery version.

In the modern era, cheaper plastic items often attempt to mimic more expensive wooden and metal products though they are only skeuomorphic if new ornamentation references original functionality, such as molded screw heads in molded plastic items. Blue jeans

Jeans

Jeans are trousers made from denim. Some of the earliest American blue jeans were made by Jacob Davis, Calvin Rogers, and Levi Strauss in 1873. Starting in the 1950s, jeans, originally designed for cowboys, became popular among teenagers. Historic brands include Levi's, Lee, and Wrangler...

 have authentic-looking brass rivet caps covering the functional steel rivet beneath; digital cameras play a recorded audio clip of a conventional SLR camera mirror slap and shutter click. Such ornamentation is not necessarily non-functional: the camera shutter sound is used to indicate to subject and photographer when the taking of the picture is complete.

Other examples:

• Decorative stone features of Greek temple
  Greek temple
  Greek temples were structures built to house deity statues within Greek sanctuaries in Greek paganism. The temples themselves did usually not directly serve a cult purpose, since the sacrifices and rituals dedicated to the respective deity took place outside them...
  
  s such as mutules, guttae, and modillions that are derived from true structural/functional features of the early wooden temples
• Ornamental pylons framing modern bridges, such as the twin 89 metre pylons at each end of the Sydney Harbour Bridge. They do not support anything, and are there only to frame the structure itself and make it look more like a traditional bridge: http://en.wikipedia.org/wiki/Sydney_Harbour_Bridge#Pylons
• An early pottery butter churn, at the Jaffa Museum, shaped rather like an American football, imitating the shape of its predecessors, which were made of hide.
• Injection-molded plastic sandals that replicate woven strips of leather
• Artificial film grain
  Film grain
  Film grain or granularity is the random optical texture of processed photographic film due to the presence of small particles of a metallic silver, or dye clouds, developed from silver halide that have received enough photons. While film grain is a function of such particles it is not the same...
  
   added to digitally-shot movies to give a softer, more expensive effect and the expected "shimmer" of the grain pattern between successive frames
• Various spoke patterns in automobile hubcaps and wheels leftover from carriage wheel construction
• Fake woodgrain printing on thousands of modern items of plastic, Formica, or pressboard furniture
• Fake stitching in plastic items that used to be made of leather or vinyl and actually stitched together
• Tiny, non-functional handles on small maple syrup
  Maple syrup
  Maple syrup is a syrup usually made from the xylem sap of sugar maple, red maple, or black maple trees, although it can also be made from other maple species such as the bigleaf maple. In cold climates, these trees store starch in their trunks and roots before the winter; the starch is then...
  
   jugs
• A fiberglass boat with striations made to look like wood planking
• The non-functional scoops on numerous automobiles, notably supercharger
  Supercharger
  A supercharger is an air compressor used for forced induction of an internal combustion engine.The greater mass flow-rate provides more oxygen to support combustion than would be available in a naturally aspirated engine, which allows more fuel to be burned and more work to be done per cycle,...
  
   scoop
  Hood scoop
  A bonnet/hood scoop is an upraised component on the hood of an automobile that either allows a flow of air to directly enter the engine compartment, or appears to do so. It has only one opening and is closed on all other sides...
  
   on the second generation Mini-Cooper, and nearly all rear wheel brake scoops on Ford Mustangs of any vintage.
• Elaborate lacing on children's Velcro-secured shoes
• Bowsprit
  Bowsprit
  The bowsprit of a sailing vessel is a pole extending forward from the vessel's prow. It provides an anchor point for the forestay, allowing the fore-mast to be stepped farther forward on the hull.-Origin:...
  
  s mounted on the bows of steamships (which, having no sails, require no rigging)
• Impressive, large-diameter concentric assemblages of black and silver "hardware" encircling the tiny objective lenses on most consumer-grade digital still and video cameras
• Cigarette
  Cigarette
  A cigarette is a small roll of finely cut tobacco leaves wrapped in a cylinder of thin paper for smoking. The cigarette is ignited at one end and allowed to smoulder; its smoke is inhaled from the other end, which is held in or to the mouth and in some cases a cigarette holder may be used as well...
  
  s with the paper around the filter
  Cigarette filter
  A cigarette filter has the purpose of reducing the amount of smoke, tar, and fine particles inhaled during the combustion of a cigarette. Filters also reduce the harshness of the smoke and keep tobacco flakes out of the smoker's mouth.-History:...
  
   printed to look like a cork filter
• Hopper of a digital slot machine
  Slot machine
  A slot machine , informally fruit machine , the slots , poker machine or "pokies" or simply slot is a casino gambling machine with three or more reels which spin when a button is pushed...
  
  
• Non-functional "fake" window shutters

Digital skeuomorphs

Computer interfaces, pictures of buttons that appear to move up and down, files and folders that look like real world objects, added to operating systems that formerly had a command line input.
Many music and audio computer programs employ a plugin architecture, and some of the plugins have a skeuomorphic interface to emulate expensive, fragile or obsolete instruments and audio processors. Functional input controls like knobs, buttons, switches and sliders are all careful duplicates of the ones on the original physical device being emulated. Even elements of the original that serve no function, like handles, screws and ventilation holes are graphically reproduced.

The arguments in favor of skeuomorphic design are that it makes it easier for those familiar with the original device to use the digital emulation, and that it is graphically appealing.

The arguments against skeuomorphic design are that skeuomorphic interface elements use metaphors that are more difficult to operate and take up more screen space than standard interface elements; that this breaks operating system interface design standards; that skeuomorphic interface elements rarely incorporate numeric input or feedback for accurately setting a value; and that many users may have no experience with the original device being emulated.

Skeuomorphism is differentiated from path dependence

Path dependence

Path dependence explains how the set of decisions one faces for any given circumstance is limited by the decisions one has made in the past, even though past circumstances may no longer be relevant....

in technology, where functional behavior is maintained when the reasons for its design no longer exist.