The meaning of IM is to send an instant message to. How to use IM in a sentence. Instant messaging (IM), sometimes also called messaging or texting , consists of computer-based human communication between two users (private messaging) or more (chat room or group ) in real-time, allowing immediate receipt of acknowledgment or reply. IM is short for instant message, a message directly sent from one person to another. IM is also short for Instant Messenger, a program that connects users to the Internet or network to send text messages. IMDb is the world's most popular and authoritative source for movie, TV and celebrity content. Find ratings and reviews for the newest movie and TV shows. Get personalized recommendations, and learn where to watch across hundreds of streaming providers. (Definition of IM from the Cambridge Advanced Learner's Dictionary & Thesaurus © Cambridge University Press) What does IM stand for? IM abbreviation. Define IM at AcronymFinder.com. This disambiguation page lists articles associated with the title IM. If an internal link incorrectly led you here, you may wish to change the link to point directly to the intended article.