Explaining the difference between raster and vector is one of the most common discussions I have with my clients. Mostly, when they do not understand why a small JPG file they pulled off the Internet will not enlarge on their printed flyer.   Or when they only have a low quality PDF of their logo, when what they really need is an .AI or .EPS file.  This infographic below should help explain the difference (and importance) of raster and vector images.