To the user, an icon is a small graphical image that represents an application when that application's main window is minimized. For example, Microsoft Paintbrush uses an icon that looks like a painter's palette to represent its minimized window. Icons are also used in message and dialog boxes.
To the application, an icon is a type of resource. Before resources are compiled, each icon is a separate file that contains a set of bitmap images. The images may be similar in appearance, but each is targeted for a different screen device. When you want the application to use an icon, have the application request the icon resource by name. Windows then determines which of that icon's images is most appropriate for the current screen. Because Windows handles this operation, the application need not check the screen type or determine which icon image is best suited for the current screen. The following figure illustrates what happens when an application requests an icon resource.