"The Common UNIX Printing System, or CUPS, is the software you
use to print from applications like the web browser you are using
to read this page. It converts the page descriptions produced by
your application (put a paragraph here, draw a line there, and so
forth) into something your printer can understand and then sends
the information to the printer for printing.
"Now, since every printer manufacturer does things differently,
printing can be very complicated. CUPS does its best to hide this
from you and your application so that you can concentrate on
printing and less on how to print..."