Whatever is the placeholder for the actual image name. Meaning "whatever" image you are using. Here's an actual example, keep in mind there are many ways to use the background property.
background:#fbfbfb url(background.png) repeat-x;
In this example the background colour and image is set, and it will only repeat on the x axis. The background colour (#fbfbfb) will fill the entire area of the object the css property is acting on.