iTunes is a proprietary digital media player application, launched by Apple Computer in 28 April 2003, for playing and organizing digital music and video files. The program is also the interface to manage the music on Apple's popular iPod digital audio player. Additionally, iTunes can connect to the iTunes Music Store (sometimes referred to as "iTMS") which allows users to purchase digital music and movie files that can be played by iPods and iTunes.
iTunes has gained and maintained a reputation for being easy to use while still providing many features for obtaining, organizing, and playing music. The program is freely downloadable, bundled with all Mac computers and iPods, and supplied with Mac OS X.
iTunes is compatible with computers running Mac OS X, Windows 2000, Windows XP, and Windows Server 2003 operating systems. The program was initially developed on Mac OS 9, but OS 9 support was discontinued with the release of iTunes 3; in addition, no version of iTunes has supported a non-NT based Windows release such as Windows 98 or Me. There has been some success running iTunes under Crossover Office on Linux, a Wine variant.
iTunes originally had a brushed metal interface, but with the introduction of iTunes 5.0, it now has a new, thinner interface commonly referred to as "plastic" and is based on the Unified look from Mac OS X v10.4, but darker.
Source: Wikipedia.org