Definition: BitTorrent

A popular protocol for sharing large files over the Internet, developed by Bram Cohen in 2001 and available for all major platforms. There is no centralized server. Each BitTorrent user becomes a source for another user who wants the same file. The BitTorrent client balances the load on the user's computer because downloading is faster than uploading.

Widely used to transfer pirated movies and software, BitTorrent and other file sharing systems accounted for more than half of Internet traffic around the turn of the century. After movie streaming from Netflix, YouTube and other legal sources became popular, BitTorrent traffic dropped dramatically.

Torrents
A torrent was originally a file of metadata on a BitTorrent server that keeps track of where all the files are. In practice, torrent refers to any file transferred via BitTorrent, and large files are broken into smaller ones.

File sharing systems have been architected in different ways as outlined in the following illustrations. See peer-to-peer network, Napster and KaZaA.

BitTorrent Leechers and Seeds

A "seed" is a BitTorrent client that has the file. A "leecher" is a BitTorrent client downloading, who then becomes a seed for someone else. However, a "leech" is a user who exits the program immediately after downloading to prevent being a seed.