I'm not sure if you watch star trek, but torrents are kinda like the borg.
If not, torrents are kinda like a cluster of servers that share the load, but instead of cpu/memory, they share bandwidth.
Lets say you have a 1.5GB file that you want people to download. Normally you would have to host that on your website. Well, you get 5 - 10 people downloading that file and your site is pretty hosed because everyone is eating your bandwidth.
With bit torrents, you have someone who seeds the file, so user 1, 2 and 3 start getting it. Lets say user 4 connects to the share and wants the same file, well instead of downloading from the master, he starts to download parts of the file from user 1, 2 and 3, splitting the load amongst all the users instead of a single point.