Pandora, according to Pandora.com:
Pandora is a music discovery service designed to help you enjoy music you already know, and to help you discover new music you'll love.
Basically you can choose the specific genre or style of music you wish to listen to and it automatically begins to serve you your preference. Pandora uses the Music Genome Project. The Genome Project was started in early 2000 and works with the "DNA" of songs using a large group of highly skilled musicians. Unfortunately anyone outside the US will not be able to take advantage of this brilliant product until such a time as online copyright and licensing issues are resolved
Delivery of Pandora is based on proper licensing from the content rights holders - we have always believed strongly in honoring the guidelines as determined by the artists, labels and publishers. In the U.S. there is a federal statute called the Digital Millennium Copyright Act (DMCA) that provides this license for all the music you hear on Pandora. Unfortunately, there is no equivalent license outside the U.S