PostScript is a language for output devices.  It does for output
devices what Unix does for processors, viz., it allows a common
software interface despite differences in hardware platform.
PostScript controllers exist for paper printers from 4 pages
per minute up to 92 ppm, from 300 dots per inch to over 6000 dpi
typesetter, and for film recorders, color printers and X Window
terminals.  Without PostScript, every text formatter has to
understand the idiosyncrasies of every vendor's hardware.
See comp.lang.PostScript for more.  PostScript is a registered
trademark of Adobe Corporation.