BitTorrent is another Peer-to Peer (P2P) file sharing system or protocol. BitTorrent offers a way to share large files or data.
  When data is shared using BitTorrent system, pieces of the files are stored in many places and also shared from many places.

   In turn each person receiving the data can share it with others. This offers a way to get large files of data without someone having to host it and one person paying the hardware costs and bandwidth costs.  

   The good thing is that it keeps the pressure off of the original data distributor and spreads it our over the many people who have the data stored on their computers. With a lot of people sharing the same file, if one computer fails it will not collapse the whole system.

  As you can imagine this has caused a large increase in traffic on the internet. Bram Cohen came up with this protocol back in April of 2001 and released it on the web in early July, 2001

   The whole shebang is owned by his company BitTorrent, Inc.
Since it's inception there have been a lot of compatible "BitTorrent clients" written.
They are available in different computer programming languages and computing platforms.

   As you can imagine legal issues have cropped up.
BitTorrent trackers are a topic of concern. BitTorrent isn't illegal but it can be used illegally to share copyrighted stuff.
Some websites have been sued and closed down as a result of this.

   HBO is in the middle of an attempt to stop people from sharing it's movies and TV shows.
They have sent "cease and desist" letters to ISP providers to stop their customers from using the ISP to do the downloads. They have even resorted to injecting bad data into one BitTorrent of a show called "Rome". The movie business made a deal with BitTorrent in 2005 that would cut down on the problem of movies being distributed.

  They don't have a way to search for files by name. that has to be done on a regular search engine so this keeps them away from the legal entanglements that would be there if they actively worked to implement the illegal aspect of there data sharing.
They also don't hide the information about who is sharing what.    See www.rc123.com even more tips...