At today's iPad event, the high definition Retina Display was first off the blocks in a set of features that make up the next generation device. This upgraded display has the 9.7-inch screen of the iPad set at 2048 x 1536 pixels, this being "for the first time an iPad has a higher resolution than even the display behind me" as Apple's Eddie Cue noted. This display has "1 million more pixels than HDTV" Apple touted, with "264 pixels per inch in this display, and that's enough to call it a Retina Display."
This display is essentially what you're getting already with the iPhone 4S, it having the ability to trick your eye into not being able to discern individual pixels - they're so small that your normal human eye can't detect them. This is 44% greater saturation than the past model, all of this backed up by A5X quad-core graphics - that's also an improvement over the past model iPad with its A5 chip.