XDCC (Xabi DCC or eXtended DCC) is a computer file sharing method which uses the Internet Relay Chat (IRC) network as a host service.
XDCC was initially a script written in 1994 for ircII. This script extends the ircII DCC command. Now XDCC refers to IRC bots running file sharing programs in general. XDCC bots serve one or more usually large files for download using the DCC protocol.
Unlike peer-to-peer transfers, XDCC servers are often hosted on connections with very high upstream bandwidth, sometimes in excess of 100 Mbit. Often FTP servers are also running on the XDCC servers to facilitate uploading of materials to them.
To use XDCC, one can send a private message (query) or send a CTCP command to a bot, using an IRC client. The user can ask a bot what files it has by private messaging "xdcc list" to the bot. However, this feature is often disabled as to not attract too much attention. When a user wants to download a packet or file from a bot, the user would type something such as "xdcc send #<pack number>" to the bot. The bot will either start sending the user the packet or the bot will place the user in a queue, and force the user to wait their turn.
Addons exist, such as XDCCKlipper (for mIRC) which listen to adverts listed in a channel by the bots and save them to a separate window to facilitate easier browsing and allow users to view the status of a bot (speed, queues, slots etc.).
See XDCC Commands