More known as IRC. Internet Real time chat thingie, in which a group of people use their computers to talk to other people. The best way to communicate over the internet next to sending emails.
There are diffrent "rooms" which you can join and there are also diffrent "net's".. The most popular is EFnet.
For newbies and lazy humanoids there are diffrent software to help them out, the most common one is Mirc for Windows based systems.