A popular, distributed form of peer-to-peer file sharing that enables a client program to fetch different parts of a file (a "torrent") from different sources in parallel. The system is designed to encourage users to make downloaded data available for others to upload. This is aided by a scheme for exchanging unique identifiers, commonly stored in ".torrent" files. A downloader who does not serve data to others is called a "leech". A "seed" is a computer that has a complete copy of a file, possibly the original. Most of the data is copyright material like films or commercial software.