Screen density refers to the number of device pixels on a physical surface. It is often measured in pixels per inch (PPI). Apple has coined the marketing term Retina for its double-density displays. According to Apple's official website:
"Retina display's pixel density is so high your eye is unable to distinguish individual pixels."
In other words, the retina display has a high enough pixel density to prevent pixelation to be noticeable to the human eye. But, because these displays are being widely implemented and used, it is more important than ever to create websites and apps that support these displays.
In the following figure, we compared the pixels between Retina and a standard definition display. In Retina ...