"Skeumorphism" is a design technique which refers to making an object resemble something else. A strong, underlying design principle for iOS and its user interface, Apple has designed icons and apps to resemble real-life objects for a long time. Initially, making iBooks look like an actual wooden bookshelf was intended to help new users grow accustomed to navigating smartphones with ease.
However, with the rise in popularity of the smartphone, it is safe to say guiding users through the learning curve of using the device is no longer necessary. According to the Wall Street Journal, Apple will be abandoning skeumorphism with the new user interface for the next iteration of iOS. More plain, solid backgrounds as well as more white space are expected to be favored.
Besides the flatter, starker design change, iOS 7 is also expected to come with a greater focus on sharing photos and videos as well as the rumored iRadio service which major music labels have purportedly signed on for. We will have more concrete news in a while as WWDC gets underway.