What is the relationship between Silver Light, WPF and XAML?

As explained previously XAML is a XML file which defines the UI elements. This XML file can be read by WPF framework or Silver light framework for rendering. Microsoft first developed WPF and they used XAML files to describe the UI elements to the WPF framework. Microsoft then extended WPF and made WPF/e which helped to render the UI in the browser. WPF/e was the code name for Silver Light. Later Microsoft launched Silver Light officially.
So the XAML just defines the XML structure to represent the UI elements. Both the frameworks i.e. WPF and Silverlight then reads the UI elements and renders the UI elements in the respective platform.