The Bit Torrent system is a download mechanism, in which you download from others who have already downloaded the same file (peers), instead of straining one download server.
How it works:
– You download a .torrent file (mostly from the tracker itself), which has some info and a link to the tracker server.
– The tracker server.. well, tracks each and every peer; the people who are downloading or have downloaded. Your torrent program connects to this server and requests a list of peers.
– Your program then connects to the peers which have already downloaded parts of the file, which you still have to get. Most programs connect to a dozen peers at the time.
– You then keep repeating to download little parts from others, and others download from you, until you have a complete file.
This mechanism keeps the bandwidth down for the servers, and still allows distribution of files.
However, Torrents have become very popular with software/media pirates, because the file itself will never be located on a central server, instead, it will be split over hundreds of computers. This means you can’t tackle it easily by shutting down one server, and because the tracker doesn’t have a physical copy of the file itself, its not doing anything illegal.