Internet Relay Chat – IRC is an old open protocol that was used extensively for communications between government and university systems, and other research institutions. It is a text-based system of servers and channels (chat rooms). It is still in use today, and is used for general chat purposes among users, as well as for collaborating on open source projects and other projects, including clubs and organizations. IRC is starting to see increasing use in corporations.
Here's a good, detailed page with information on IRC: https://en.wikipedia.org/wiki/Internet_Relay_Chat