Zune is a Microsoft entertainment platform and portable media players. The Zune entertainment software platform and supporting products designed and marketed by Microsoft include Zune Marketplace Software, the Zune Social, Windows 7 Media Center (Podcasts only) and Xbox 360 (TV & Movies). Zune Marketplace Software offers music, TV shows, movies, podcasts, and music videos. The Zune Social is a service integrated with Xbox Live that allows users to manage friends, send messages, and compare music. Each user has a personal Zune Tag, which corresponds with their Xbox Live Gamer Tag if they have one. Zune Social allows two Zunes to send songs wirelessly, but with extensive DRM restrictions.
The Zune software is used to manage the Zune, and runs exclusively on Windows XP and later. It can rip CDs, manage music and can be used to access Zune Marketplace. Purchasing items from it requires Microsoft Points or a Zune Pass. Zune Pass is a subscription music service that allows the user to temporarily download an unlimited amount of songs for the length of the Zune Pass subscription, as well as permanently keep up to 10 tracks per month.
Zune's distinguishing features are its FM radio, subscription model, and the Zune Social. FM radio is available on all Zune hardware models, while Zune HD also features HD radio. FM radio features include RBDS, which receives and displays digital information in conventional FM radio broadcasts. Files can be shared wirelessly between Zunes and PCs as well as other Zune devices. Zune's primary competitor is the Apple iPod product line.
Source: http://en.wikipedia.org/wiki/Zune