An output device for translating information from a computer into pictorial or graphical form on paper or a similar medium.

Formerly, plotters used pens to mimic human technical drawing. One of the simplest implementations was the flatbed plotter. One or more pens were mounted on a carriage that could be moved to precise positions on a bar that spanned the width of the medium, i.e. the x-axis. The bar was mounted so that it could be moved precisely on tracks that lay parallel to the lengthwise edge of the medium, i.e. the y-axis. It was thus possible to move the pen to any point that lay within the available range of x and y coordinates. The pen could either touch the surface as it moved, thus producing a line, or it could be lifted off the surface as it moved. When drawing a diagonal line the computer generally had to provide only the coordinates of the start and finish points. For larger drawings a drum plotter was often used. The drawing method was the same, but the medium was wrapped around part of the drum surface and was often wound onto take-up spools on either side of the drum axis.

Such plotters are now rarely used. Standard laser and inkjet printers can produce the same results more quickly, cheaply, and flexibly. Modern dedicated plotters generally use inkjet technology and are distinguished by their ability to handle large paper sizes and to accept input in special-purpose plotting languages.