Skeuomorphism is the imitation of a physical object
Skeuomorfisme or Skeuomorfisch design is the practice of imitating a physical object in computer programs/apps: This is done in order to give it a familiar look. The term has become known by IOS version 6 and earlier: A note app that features a ring band with tearable leaves, the iBookstore that shows books in a wood bookcase. Proponents of the skeuomorfisme think that using known materials increases the Gebruiksgemakt: In a book you are used to storing the leaves, so this is also done in a digital book (sometimes even with sound effect). This seems familiar, even if it has no (direct) utility.
TEDxManchester-Dan O'Hara-Skeuomorphism [YouTube] KpFKsC4mi5I [/youtube]