Retina display is a term used by Apple for a high- resolution display like the one used in the iPhone 4 and iPad 3 . Retina displays work with In-Plane Switching( IPS) and are characterized by a wide viewing angle.
The resolution of Apple's Retina display is a few hundred pixels per inch. In terms of the screen size of an iPhone, this results in a resolution of 960 x 640 pixels, quadrupling the previous 480 x 320 pixels, and 2,048 x 1,536 pixels for the iPad 3.
Apple chose the name Retina display because the pixel size and the dot spacing between the pixels are so tiny that the human eye cannot distinguish and see them: exactly 0.078 mm.
The image quality of the Retina displays is derived from the higher pixel density, the improved contrast with brighter whites and darker blacks, the in-plane switching technology with the wider viewing angle, the specially treated surface glass and the backlight, which provide for more brilliant displays.