This means that in low light situations, the pictures should be exposed better, with less noise, and more definition. In fact, Google's folks said that this imaging sensor was designed for camcorders, and is "unprecedented" in a mobile phone, though it might have been the marketing team speaking. We found a Sony IMX377 1/2.3" sensor that is 12.3 MP with 1.55 micron square pixels, meant for compact cams, which might be the one they were referring to, and are providing its specs in the slideshow below. The camera unit comes with f/2.0 aperture.
Thanks to the new sensor, the Nexus 5X and 6P will be able to deliver 4K video recording (of course), as well as slow-motion video capture, it's just that the 5X will do it at 120 frames per second, while the 6P can do 240 fps slow-mo, pretty cool. Along with HDR+ and the new photo album and Camera app shenannigans, the new phones should finally usher the Nexus line at the top of mobile photography.