Rapid stop and go typing that one does when instant messaging. Can be identified by the tell tale sounds of:

tappity-tappity-tappity-tappity-tappity-tap-tap-tap-CLICK
*pause*
tappity-tappity-tappity-tappity-tap-tap-tap-CLICK
*pause*
tappity-tappity-tap-tap-tap-tap-tap-tap-tap-tap-CLICK
and so on...

Named because it sounds like and has a similar rhythm to firing an automatic weapon. Usually not that annoying, but can be incredibly irritating when done by that lazy co-worker always slacking off at work or that college roommate that IMs until 5am every night.
Also known simply as "machine gunning".

the thing that you don’t have when you’re phones percentage is over 20