During the specialize pass of Windows Setup, machine-specific information for the image is applied. For example, you can configure network settings, international settings, and domain information.
The specialize pass is used in conjunction with the generalize pass. The generalize pass is used to create a Windows reference image that can be used throughout an organization. From this basic Windows reference image, you can add further customizations that apply to different divisions within an organization or apply to different installations of Windows. The specialize pass is used to apply these specific customizations.
For example, during the specialize pass, you can specify different home pages in Internet Explorer for different departments or branches within your business. This setting will then override the default home page that was applied during the generalize pass.