All Images existing on the faces of earth have only 2 basic unit cells: Pixels or Dots.  Vector Images have their Key element as Dots, hence they offer Infinite zoom without Blur. These can be re-sized without compromising quality and are often used for creating logos and other graphics that need to go across various outputs (from Pamphlets to billboard). Corel Draw and Illustrator outputs are Vector Images.Raster images (also called bitmap images) are made up of Square pixels which allow zooming to only one extent. After that, the image blurs. Hence these images can not be used for Large Board Printing. Also,  re-sizing is a major issue here. Photoshop Outputs and all Photographs are Raster Images.