Wikipedia defines a skeumorph as:
a derivative object which 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.
Steven Poole wrote a great article a couple of days ago in which he attacks user interface chrome–not Google’s browser, but the graphical interface: the buttons, the tabs, the switches, the scrollbars, the menus and so on. He points out that a lot of chrome tries to resemble physical objects: buttons that look like actual buttons, digital books that resemble physical books with pages drawn on the side, music apps that actually draw cables you have to move around. This of course varies to a great extent from app to app, but generally we often see interfaces that try to look like physical objects to seem more familiar.
Essentially what we’re seeing are skeumorphs. Designers using the real world as a guide for the graphical interface. Of course this was very effective when the first GUI was introduced. It gave the user a sense of familiarity–a way to figure out how the stuff on the screen could be used and manipulated. Poole argues that this is no longer necessary, especially on touch devices where the only thing you can do is touch the screen.
I agree that the real world metaphor isn’t strictly necessary for a successful interface. After all, the Web is a pretty interactive place these days, but it usually doesn’t resemble much of the real world. What is necessary is a level of consistency. Things that can be touched or clicked should be identifies as such, and that visual cue should be consistent throughout the interface. While iBooks might look great the first time you use it, as you begin to actually read, you realize that all the interface cruft doesn’t help at all, which is why I think the Kindle UI is so much better. It’s almost as if the interface is ashamed of being digital–losing the aesthetic of the past and transforming into something new, something designed for the new medium.
I think Poole didn’t go quite far enough though. What we lose by using too much of the physical metaphor isn’t just screen space, it’s innovation. We represent things as they would look like in the real world, and by doing so we bind ourselves to those limitations–we design the solution within that frame. Poole gives an absurd example from Reason–an interface where cables have to be moved manually, using the mouse. I especially dislike the latest set of interfaces from Apple for the iPad. They look great, but they cling to the physical look far too much, losing the opportunity to create a fresh look in the process.