The dogcow is a drawing of a rather indiscriminate-looking animal (it looks mostly like a dog but is said to have the spots of a cow) that is or has been used in the Apple MacIntosh operating system to help tell users about their printing options. You can see the dogcow by going to the Finder, looking under "Page Setup...", and then looking under printer options. The dogcow is used to show you what kind of option you've selected. For example, "Flip Horizontal" flips the dogcow to upside down.
If you click on the dogcow, Macintosh sends you the animal's characteristic cry of "Moof"! The dogcow icon was originally created by graphic artist Susan Kare. (She is also the artist who created the graphic interface for everyone's favorite Windows 3.1 card game, Solitaire.) Microsoft has adopted its own version of the dogcow and uses it to demonstrate slide transitions in its PowerPoint application, although Apple retains its copyright on the original image and, believe it or not, the "Moof"!
OS X creators originally dropped the dogcow, but on-line petitions and press coverage designed to "bring back the dogcow" have made Apple executives aware of the tremendous cult following of this hybrid icon. (Legend has it that development teams at Apple still use the dogcow to identify a partly completed program that is unique and worth checking out.) It is expected that the dogcow will return in the next version of OS X.