Retina Display refers to high pixel density displays with pixel densities of 300 ppi or greater. The iPhone 4 in 2010 was the first device to feature a Retina Display. Retina Displays split each pixel into four to reduce pixelation. Supported devices include various iPhones and iPads with resolutions ranging from 960x640 to 2880x1800. Designing and developing for Retina requires exporting images and vectors at double the resolution and using techniques like media queries for background images.