@akamran @gwendolenau
Bittorrent is a protocol for sharing large fixed files that takes advantage of the upload bandwidth of those who are trying to download a copy of the file.
To take a simple and safe example, libreoffice is a relatively large application so they have torrent links on their download page.
https://www.libreoffice.org/download/
if you have a torrent application installed for example
https://transmissionbt.com/
after you download the torrent file it should load into the torrent downloader application which will connect to a "tracker" server to see what other computers that have parts of the file you're interested in to download from.
But your computer will also announce to the tracker what parts you have and someone might download them from you.
For things like free software downloads or archives of big things like wikipedia this is all totally fine.
peertube internally uses bittorrents to help share the load of distributing the video file, so if one video became popular others watching the video can share parts so the primary host doesn't get crushed needing to serve more data than what the cheap server can support.
However people often want to share commercial movie, music, and tv files and because the default behavior of bittorrent shares your IP address, a motivated company can force your ISP to turn over your account information over to the law suit happy media companies.