From The Free On-line Dictionary of Computing (8 July 2008) [foldoc]:
Internet Relay Chat
IRC
<chat, messaging> (IRC) /I-R-C/, occasionally /*rk/ A
client-server chat system of large (often worldwide)
networks. IRC is structured as networks of Internet
servers, each accepting connections from client programs,
one per user.
The IRC community and the Usenet and MUD communities
overlap to some extent, including both hackers and regular
folks who have discovered the wonders of computer networks.
Some Usenet jargon has been adopted on IRC, as have some
conventions such as emoticons. There is also a vigorous
native jargon (see the entry for "chat").
The largest and first IRC network is EFNet, with a smaller
breakaway network called the Undernet having existed since
1992, and dozens of other networks having appeared (and
sometimes disappeared) since.
See also nick, bot, op.
{Yahoo's IRC index
(http://yahoo.com/Computers_and_Internet/Internet/Chat/IRC/)}.
(1998-01-25)
From Jargon File (4.4.4, 14 Aug 2003) [jargon]:
IRC
/I.R.C/, n.
[Internet Relay Chat] A worldwide "party line" network that allows one
to converse with others in real time. IRC is structured as a network
of Internet servers, each of which accepts connections from client
programs, one per user. The IRC community and the Usenet and MUD
communities overlap to some extent, including both hackers and regular
folks who have discovered the wonders of computer networks. Some
Usenet jargon has been adopted on IRC, as have some conventions such
as emoticons. There is also a vigorous native jargon, represented in
this lexicon by entries marked `[IRC]'. See also talk mode.