Its the path providing facility to provide the virtual content to compiler. For example, a virtual path provider provides a means to supply content from locations other than the file system.
To attain the same following step(s) are required :
1. Create a VirtualPathProvider class, and implement all the required methods to handle files and folder requests.
2. Register the virtual path provider to let the ASP.NET hosting environment know where the content will be served from.
3. Create VirtualFile and VirtualDirectory objects to stream the content.
For more details, visit http://support.microsoft.com/kb/910441