IRC (Internet Relay Chat) lets you take part in real time online, typed "conversations" with people from all over the world through the Internet.
A wide variety of topics are discussed on IRC's. The discussion can resemble anything from a polite chat among good friends to an intense business conference. When you type a comment, it appears almost instantly on the other people's screens, no matter how far away. The other people in the discussion can then type in a response, which can be seen by you just as quickly.
IRC is similar to talking over the telephone, but you are typing what you want to say instead of speaking, and usually chatting with a group of people instead of one individual.