BitTorrent is a way to transfer files of just about any size quickly and efficiently. It works by breaking files up into small pieces. The file is downloaded piece by piece from one or many different sources. It's efficient because you get faster downloads using a lot less bandwidth. The name BitTorrent is also used to describe the official BitTorrent client. When you use BitTorrent, you make, distribute and get files. To make and share a file or group of files through BitTorrent, you first make it into a “torrent"--a small file which contains information about the files and about the computer that coordinates the file distribution. Others (refered to as "peers" ) find and open your torrent and begin downloading the pieces. As the file downloads to peers' machines, those peers also share the pieces they get with even more people who are also trying to download the same file. This sharing makes the file easier to download as more parts become available from multiple sources. Since the file is broken up into small pieces, little bandwidth is used to do the overall transfer. Once the file is finished downloading, the client software continues to share the completed file (becoming a "seed" ) with others looking for it. This also means the file can still be downloaded long after the original poster has stopped seeding the file.http://www.bittorrent.com/help/faq/concepts