A technology that gives users the ability to identify people online and to exchange messages with them in real time. Referred to by many as the "coolest way to communicate online since e-mail," it typically works like this: The instant messaging system alerts you whenever somebody on your "buddy list" is online and trying to contact you via your computer; you can then initiate a chat session with that person and type text messages back and forth.
Instant messaging is considered more spontaneous than e-mail or chat rooms, and you can even surf the Web together while having a real-time text conversation at the same time.
There are several competing instant messaging services, and unfortunately, there's no standard; the people you want to "instant message" with must use the same IM system that you use. Another downside is that instant messaging is not yet designed for secure use.