BitTorrent is a content distribution protocol that enables efficient software distribution and peer-to-peer sharing of very large files, such as entire movies and TV shows, by enabling users to serve as network redistribution points.
BitTorrent's protocol has been described as a "swarming, scatter and gather" file transfer protocol. Rather than having to send a download to each customer requesting it, the distributor or holder of content sends it to one customer who, in turn, sends it to other customers. Clients share pieces of the download back and forth until everyone has the complete download. This distribution scheme makes it possible for the original server to handle many requests for large files without requiring immense amounts of bandwidth.
Bram Cohen wrote BitTorrent in Python and made it available in 2001. BitTorrent is distributed freely under an open source license.