LaserJets, like many other printers, print in lines per inch (Ipi). The lines represent in digital image printing lines of pixels. If the pixels are printed squarely than each square area (of a width equal to that of the actual line width) must be printed with a desired amount of ink variations in order to generate the gray levels (see John Russ’ book for a nice illustration on how this is done in a LaserJet). LaserJets and Inkjets use dots as the smallest printed entity.