Silverlight application
The Silverlight application web part generates a container that can be used to display a Microsoft Silverlight application on the website. The web part is not configured to display anything on this page. You can either configure it to display an application of your choice, or view a working example on the Silverlight page of the sample E-commerce Site.
More information can be found in Kentico CMS Developer's Guide -> Development -> Microsoft Silverlight integration.