IRC (internet relay chat) is how people communicate via chat rooms. If you log onto an IRC server, you can join different chat rooms and talk to people without needing to know who they are or what their IM addresses are. Our Live Chat on this site is an example of IRC. If you were to join our chat room, there would be a list of people that are logged in, and there might be a conversation going on. You could join in on the existing conversation, or ask a question, or even just say "hi" and see if you get a response. IM, or instant messaging, is really more like a phone call - you're typically talking to just one person in an IM window (unless you conference several together), and you need to have a specific address in order to contact someone. I use both IRC and IM. In IRC, I join a number of chat rooms, or channels, that are dedicated to providing computer support, as well as some that were created just for the purposes of friendship. Once in the room, I can talk to anyone else that's there. I also use IM as a means of talking to specific people, especially when I haven't joined any chatrooms.