BitTorrent is a widely-used peer-to-peer file-sharing protocol, invented by Bram Cohen in 2001. BitTorrent is mostly decentralized, and is optimized for transferring large files. A substantial fraction of internet traffic uses the BitTorrent protocol.
For originators of the content, BitTorrent is more bandwidth-efficient, because most content consumers can download from peers rather than from a centralized server. For this reason, many Linux distributions publish CD images via BitTorrent. But the protocol has attracted criticism because it is commonly used for copyright infringement.
This tag is for the BitTorrent protocol or BitTorrent clients in general. There is also a Windows BitTorrent client called just "BitTorrent".
Popular BitTorrent clients include