John Paczkowski interviewed Apple's Phil Schiller and Craig Federighi on the new iPads:
Similarly, since the iPad is a touch device first, touch interactions — be they via finger or Apple’s Pencil stylus — should be instantaneous, alive. And on the new iPad Pros they get pretty damn close, thanks to one of those world-of-pure-imagination innovations Apple is willing to spend years concocting. This one’s called ProMotion, and it doubles the number of times per second an image can be refreshed on the the iPad Pro’s display. Like most all mobile devices, the first-generation iPad Pro had a refresh rate of 60Hz. The new iPad Pro can ramp up to a refresh rate of 120Hz that’s more typical of 4K TVs.
Courtesy of Apple What that means in practice is that anything that moves on the device’s screen — whether it be video or a line drawing or a photo zoom — appears smoother and more detailed. Some touch interactions are dramatically more responsive; you get the sense that Apple is speeding iPad toward finger-into-puddle-of-water levels of responsiveness.