The differentiation is very simple if you remember that 'dots' refer to dots on a printed page and 'pixels' to tiny square tiles on a monitor. Both are the smallest addressable elements within their respective media. These lines are in fact rows of dots of differing sizes that give the impression of gradations in tone - we call that 'halftone'. The illusion of tone is given by the ratios of ink to paper. An area of small dots give a light tone when viewed from normal distances.
Large dots give a dark tone of whatever ink colour is being used.
No matter what the size of a dot, it is always the same colour, only its size changes based on a constant grid or matrix of the specified Lines Per Inch. We can safely ignore LPI for the minute as it has nothing to do with Web design. DPI How a laser printer emulates halftone dots using laser dots. With computer printers, dots are also used to build up an image, but in a slightly different way. Laser printers generally try to simulate the effect of a traditional halftone screen with varying sizes of dots.