A printing technique whereby ink is spread on a metal plate with etched images, then transferred to an intermediary surface such as a rubber blanket, and finally applied to paper by pressing the paper against the intermediary surface. Most print shops use offset printing to produce large volumes of high-quality documents. Although the equipment and set-up costs are relatively high, the actual printing process is relatively inexpensive.
Desktop publishing generally involves producing documents on the computer, printing out drafts on a laser printer, and then offset printing the final version. To produce the plates used in offset printing, a print shop requires either film or high-resolution paper output, which the printer can then photograph. You can obtain either by taking a PostScript file to a service bureau.