Most people think of a postscript (P.S.) as an afterthought in a letter. However, in the printing world, PostScript has totally different implications. PostScript is a text based language developed by Adobe Systems, Inc. that is used to describe how objects and text appear on a page. Such objects remain crisp even when scaled up very large. They may thus be referred to as "resolution independent."
There are PostScript files and PostScript printers. The latter are capable of reading and rasterizing the former. Non-PostScript printers depend upon software to rasterize vector graphics. Since PostScript describes a language the absence of an interpreter in the printer results in very crude low-resolution output. PostScript Level 3 printers (or interpreters) are capable of decompressing LZW compressed TIFF files on-the-fly.
Adobe fonts and drawing programs like Adobe Illustrator use embedded PostScript to display wonderful graphics on computer monitors and in print. Such may be referred to as vector graphics.
PostScript files may include the two-letter file extension ".ps" while encapsulated PostScript graphics use the three-letter extension ".eps". PostScript is a registered trademark of Adobe Systems, Inc.