Skeuomorphism and graphical interface
This design concept that Apple want to apply largely contributes to its success with the non-IT public.
This term means giving to a virtual object the appearance of a real object. The principle is widely used in graphic interfaces, with buttons like real buttons on the dashboard, progress bars and indicators that mimic the corresponding objects, the edges of window panels in relief as containing electronic equipment. These are all skeuomorphes.
The term comes from Greek skeuos, which means tool and morphos, imitate. It is not just about computing, objects of everyday life can also apply this principle. The electronic camera that emits the same sound as its mechanic ancestor is an example. Just look around to find modern objects made to have the look of old whose use is deprecated.
The metal or wood or paper textures, virtually on the screen, or actually made of plastic, are also examples of skeuomorphism. An example on this site is the green board in the XUL tutorial.
Critics say that this add nothing and it is better to make the interface more functional as possible, but in fact, the functionality leaves room for imagination. To the extent that imitation is imagination.
But there are also arguments for. Games use the principle widely in their interface to create a mood, and the same idea can be extended to utilities. New users, frightened by the technical side of computers or smartphones, will have the handling facilitated by the fact that the object has a familiar look, and it on the screen objects they already knows, and with which they knows how to interact.
The Apple firm uses extensively the principle. MacOS on his desk looks like a real office in which icons appear in relief like dropped on the screen. Most software do the same. The skeuomorphism works when not adding artificial elements, but merely gives a realistic look to the interface elements already present and without changing the mode of use.
Conversely, Windows in version 8 and particularly Android, are moving away from this concept. The reason is not clear, but given the limited success of Windows Phone, it is not certain that this is the right choice. Android having the advantage to be free and the customization, it is difficult to link its success to a graphic choice.
Updated September 20, 2013: With iO7, released in early September, Apple went in turn to "flat design", and abandons the skeuemorphisme to the same approach in the design of competing Android and Window Phone.