BitTorrent is a popular peer-to-peer (p2p) file sharing system. It is widely used to download and share large files, including software, music, movies, video games, and books. The system is often used to share files legally, such as distributing open source software disk images like Linux. It is also often used to share copyrighted material, such as feature Hollywood films, music albums, and test prep books.
GMAT Books may be available on the BitTorrent network. Downloading these files is probably illegal in your country, so proceed at your own risk. Even if it is not illegal where you are, you probably recognize that its not the right thing to do. (Think karma.) You may have trouble getting GMAT books on BitTorrent anyway, it depends if anyone happens to be sharing them at the time you look for it