torrent is slang . shorthand for a file system like "bit torrent".
Instead of downloading a huge file ( like an operating system disk iso, or a pirated movie) from one point, with special software you can download, several different parts at one time - all from different servers or computers.
Using a torrent system can make downloads faster, and it helps when people have an isp that caps their total traffic.
On the other hand, when you join a torrent net, just by installing the software, you also become one of the torrent servers. If you grab part of any file.. you become a server for that file.
-- the "fair exchange".. by downloading, you give back by serving up pieces of files you have.
Sometimes those files contain viruses, sometimes they are illegal.. and in a worst case, you may have an illegal file with embedded trackers. ( so the MMPA or FBI can prove you helped distribute illegal files)
Google and other torrent tracker search engines can help you find torrents online.