Bram Cohen created and released BitTorrent in 2001 for peer-to-peer file distribution.
BitTorrent divides a file into pieces and lets users download different pieces from multiple peers at the same time. A user can also upload already received pieces to others, distributing the workload across the swarm instead of relying on one central server. This design can make large transfers efficient when many participants share the same content.
Cohen demonstrated the protocol at the 2002 CodeCon conference. BitTorrent soon became widely associated with distributing large files, including Linux distributions and other openly shared software. The protocol itself is a technology, while a torrent file or magnet link supplies information that helps a client find peers and identify the content.
BitTorrent is not inherently illegal. Its legality depends on the material being shared and the permissions attached to it. Copyright disputes nevertheless made the protocol a major subject in Internet law and media-industry debates.