Prepress is the term used in the printing and publishing industries for the processes and procedures that occur between the creation of a print layout and the final printing. The prepress process includes the preparation of artwork for press, media selection, proofing, quality control checks and the production of printing plates if required. The artwork is quite often provided by the customer as a print-ready PDF file created in desktop publishing.
HINT:
Prepress in the context of Raster graphics
In computer graphics and digital photography, a raster graphic, raster image, or simply raster is a digital image made up of a rectangular grid of tiny colored (usually square) so-called pixels. Unlike vector graphics which use mathematical formulas to describe shapes and lines, raster images store the exact color of each pixel, making them ideal for photographs and images with complex colors and details. Raster images are characterized by their dimensions (width and height in pixels) and color depth (the number of bits per pixel). They can be displayed on computer displays, printed on paper, or viewed on other media, and are stored in various image file formats.
The printing and prepress industries know raster graphics as contones (from "continuous tones"). In contrast, line art is usually implemented as vector graphics in digital systems.
View the full Wikipedia page for Raster graphics