Resolution is a measure of graphics that's used to describe what a printer can print, a scanner can scan, and a monitor can display. In printers and scanners, resolution is measured in dots per inch (dpi)--the number of pixels a device can fit in an inch of space.
A monitor's resolution refers to the number of pixels in the whole image, because the number of dots per inch varies depending on the screen's dimensions. For example, a resolution of 1,280 by 1,024 means that 1,024 lines are drawn from the top to the bottom of the screen, and each of these lines is made up of 1,280 separate pixels--and in turn, each dot may have any number of combinations of red, green, and blue intensities.
Common resolutions in the PC world include 640 by 480 (also called VGA resolution; appropriate for a 14-inch monitor), 800 by 600 (appropriate for a 15-inch monitor), 1,024 by 768 (appropriate for a 17-inch monitor), and 1,280 by 1,024.