Online acronym, lingo for 'Internal Giggle'.
Term was created to insert realism and counter the effects of using *lol* and *lmao* too loosely when in fact most people are not actually laughing out loud or laughing their asses off but simply having an internal giggle.
Kate via IM: How was your day today.
John via IM: Fell flat on my ass today while doing a fake Karate Kid roundhouse kick yelling "Wax on, wax off". Epic fail.
Kate via IM: *ig*