A torrent file is a small file that contains metadata about files and folders to be shared over the BitTorrent protocol. Instead of downloading a file from a single source, users can download pieces of it from multiple sources simultaneously, which can speed up the process. When you open a torrent file with a BitTorrent client, it connects to other users who have the same file. This allows for efficient sharing, as users can upload and download parts of the file at the same time, making it easier to distribute large files like movies, music, or software.