For others, it's hours and hours of painstaking hard work, perfecting eye-candy that hopefully somebody will see fit to be greeted by every time the computer is used.
Wallpapers are, as they are aptly named - wallpapers for the desktop.
When you close or minimize everything, you should be at the desktop. Of course, not everybody has the same size screen. A screen resolution is the number of pixels contained on a display monitor, meaured by the amount on the vertical, and horizontal axis. The sharpness of an image depends on the size of the monitor, and the resolution. The same pixel resolution will be sharper on a smaller monitor, and lose sharpness on larger monitors because the same number of pixels are being spread over a larger space.