A new study out of the University of Ballarat in Australia has confirmed that the majority of content on BitTorrent is illegal. Researchers checked torrents from 23 trackers, the total sample consisted of 1,000 torrent files. They found that 89 percent of the files were confirmed to be illegally shared and most of the remaining 11 percent was most likely illegal. There were only three cases (it is 0.3 percent of the files) classified as legal files.
BitTorrent is a peer-to-peer (P2P) file sharing protocol used for distributing large amounts of data in Internet. BitTorrent is one of the most common protocols for transferring large files online, and it has been estimated that it accounts for roughly 27-55% of all Internet traffic as of February 2009. Source of the definition: wiki