Wiktionary
n. (context communication computing English) A computer application which allows instant text communication between two or more people through a network or the Internet in its entirety.
Usage examples of "instant messenger".
One of the keys here is a person who uses chat rooms and AOL Instant Messenger.
The AOL Instant Messenger system alone has thousands of users, hundreds of thousands of messages a day.
Kate made a mental note to block Jodi from her Windows instant messenger after hours, if the author was going to go and tattle on her.
She always kept her instant messenger signed on while she was in the office, in case one of her writers had a question.
His instant messenger program was blinking with incoming messages and as always, his e-mail was filled with notes from other Dark-Hunters.
I switched into Instant Messenger and activated the trans-world chat mode, holding my breath until the purple screen with the scrolled edges came up.