Kindle Fire HDX 8.9 tablet, and reads "Lighter than Air." The line is an obvious reference to the main hype-point of the iPad Air which is that Apple managed to slim down the tablet by nearly half a pound to get it down to about one pound. Amazon is simply reminding customers that its Kindle Fire HDX is even lighter than that, weighing in at .82 pounds.
Of course, you would likely expect the HDX to be lighter than the iPad Air since the Air has a 9.7-inch display and the top-of-the-line Kindle Fire HDX has an 8.9-inch display. If Amazon couldn't make a new device lighter when it offers that much less screen real estate, that would be something of a bungle of engineering. Of course, Amazon's Kindle Fire HDX 7 follows suit being lighter than the iPad mini 2, and once again it also has a smaller display.