A short string used to identify files shared via P2P software. You paste it into a Bittorrent client and it’ll then try and piece the file together from other users who have done the same thing.

As an example, here’s one for Warzone 2100, an excellent free open-source real-time strategy game:

magnet:?xt=urn:btih:80e5f0b142306e3b5660990c45d6406a5a259a9c&dn=warzone2100_win_x64_installer.exe&tr=udp%3A%2F%2Ftracker.opentrackr.org%3A1337%2Fannounce&tr=udp%3A%2F%2Ffosstorrents.com%3A6969%2Fannounce&tr=http%3A%2F%2Ffosstorrents.com%3A6969%2Fannounce&tr=udp%3A%2F%2Ftracker.openbittorrent.com%3A6969%2Fannounce&tr=http%3A%2F%2Ftracker.openbittorrent.com%3A80%2Fannounce&tr=udp%3A%2F%2Ftracker.torrent.eu.org%3A451%2Fannounce&ws=https%3A%2F%2Fgithub.com%2FWarzone2100%2Fwarzone2100%2Freleases%2Fdownload%2F4.4.2%2Fwarzone2100_win_x64_installer.exe&ws=http%3A%2F%2Ffosstorrents.com%2Fdirect-links%2F%2Fwarzone2100%2F4.4.2%2Fwarzone2100_win_x64_installer.exe