(via www.ubuntugeek.com)
BitTorrent is a peer-to-peer file sharing protocol used to distribute large amounts of data. The initial distributor of the complete file or collection acts as the first seed. Each peer that downloads the data also uploads it to other peers. Relative to standard internet hosting, this provides a significant reduction in the original distributor's hardware and bandwidth resource costs. It also provides redundancy against system
problems and reduces dependence on the original distributor.