Commonly known as IRC. For help, try http://www.irchelp.org. -- SunirShah
One of the first widespread chat protocols (RFC 1459), forming the biggest international chat network today, based on open standards (as opposed to proprietary stuff like AIM, MSN-IM or ICQ). Chat servers are networked together, with distributed traffic. Used today for lightweight chat, customer support, developer collaboration, etc.
http://www.irchelp.org/irchelp/rfc has more technical information.
See also: ChatLectures.
It is interesting to consider some of the [things] that have evolved out of the basic system:
How to use an IRC client:
There are two ChannelBots in #wiki, one being the requisite security bot, and thus ignorable. The other is much more interesting. DeepakGoel wrote wikibot originally for #emacs, but he has gloriously made it run on #wiki as well. It's very sexy, having already learnt all about MeatballWiki. As an example:
<Sunir> , InternetRelayChat <wikibot> InternetRelayChat --  at http://www.usemod.com/cgi-bin/mb.pl?InternetRelayChat
It can also search Google!
<Sunir> , "pet potato" <wikibot> [google] http://www.ccmuseum.org/KidsPages/potatobug.htm
See EmacsWiki:ErBot for more fun with sexy wikibot.
I love you wikibot!
the lag-monster usually tossed me into the net-split