The application icon is the most important icon for you to design. This is the place for your product identity, as well as a clear indication to the user of what your application does. The application icon is what the user opens to run your application.
There are no shape conventions for application icons. They can fill the entire icon bounding box or they can be irregular in shape. It is recommended that your icon have a three-dimensional style to it. The icons shown in Figure 4-12 are application icons used in the desktop that you can also use as templates when designing your own icons.