Users browse the web to find a torrent of interest, download it, and open it with a BitTorrent client. The client connects to the tracker(s) specified in the torrent file, from which it receives a list of peers currently transferring pieces of the file(s) … see full wiki
This review is merely for the protocol itself and not the piracy that has been attached to it.
BitTorrent is a protocol... basically a set of rules on how something should behave. You go on the Internet using a protocol called TCP and IP.
In the days of 14.4k modems and the like, the basic way to get information through the Internet was to connect to a single computer/server and get the information. That's how we get on Google, Lunch and all these other websites. You're essentially connecting to a computer that's giving you information.
Now, as higher quality movies and more digital downloads took precedence over text, a problem occurred. How can we transfer huge amounts of data to the consumers? Sure... we can set up hundreds of dedicated computers to serve this one piece of data (a movie for example). But that's too expensive. Technology is supposed to make things easier. And, it will take too long. We might as well mail them a CD!
Here comes BitTorrent. BitTorrent says, "Ok... I have this file that I want to send out. And here are 10 people that want it. I'll give Computer A the first 10% of the file.. Computer B, the second 10%... etc. As soon as Computer A gets some of the data, it'll send it out to the other computers as well."
With this approach, the originating server only has to send out 1 full copy. The rest of the "swarm" helps by sending out what they have received. This is not only cheaper for the originating server, but it's faster for the swarm. They will now have 9 places to get the information.
Unfortunately, BitTorrent has been linked to piracy. It's ease of use has allowed pirates to get what they want fast, and with little to no costs to them.
But let's not condemn the protocol. After all, we're not shutting down the Internet because of copy infringement by YouTube users, or anything else that possibly could break the law. We also don't shut down roads because there are possibly drunk drivers on the road.