IRC is Internet Relay Chat - an old form of peer communication. It is a live chat, similar to texting on an a phone. IRC is open to an unlimited number of people who can come in and out of a chat room as they please.
To join an IRC channel - you have to know which channel you want to go to - and you have to use IRC software on your computer. For Linux, there is XChat and Pidgin. Or, you can join an IRC via your browser.
The easiest way for OSE people is to go to the IRC page. Just type in your name, do the Captcha, and you are in. You will see the users on the right hand side.
We can use the opensourceecology IRC for OSE communications. Reprap is a particularly live channel, where many useful things can be found out in real time.