The pixels per inch metric went from obscure to one of the most talked about components of a smartphone display's quality the minute Apple called its iPhone 4 panel Retina Display. It coined the term on account of the factoid that at 320ppi and more, the regular human vision can't discern the individual pixels from the viewing distance you normally hold such a phone, making text crystal clear, removing any icon jaggies, and improving the overall viewing experience...Source: http://www.phonearena.com/news/Most-resolute-phones-with-the-highest-pixel-density-displays_id48823
