File Sharing
In short: File sharing is sharing files over the internet, often in peer-to-peer networks.
In more detail: The idea became known with Napster (1999). Then came eDonkey, Kazaa and BitTorrent.
In Depth
Legal situation
Distributing copyrighted works without permission is forbidden. Connection owners can be sent warning letters. Legal sharing: your own works, free licences, open source.
Technology
In a P2P network all participants download and share at the same time (torrent). Cloud links and FTP also count as file sharing in the broader sense.
See also: Torrent, Open Source, Torrent Sites