What Is Silverlight?

Silverlight enables you to create a state-of-the-art application that has the following features:
It is a cross-browser, cross-platform technology. It runs in all popular Web browsers, including Microsoft Internet Explorer, Mozilla Firefox, and Apple Safari, and on Microsoft Windows and Apple Mac OS X.
It provides a consistent experience no matter where it runs.
It is supported by a very small download that installs in seconds.
It streams video and audio. It scales video quality to everything from mobile devices to desktop browsers to 720p HDTV video modes.
It includes compelling graphics that users can manipulate—drag, turn, zoom—directly in the browser.
It reads data and updates the display, but it doesn't interrupt the user by refreshing the whole page.
Silverlight-based application with rich graphics and user interaction
Web developers and graphics designers can create Silverlight-based applications in a variety of ways. You can use Silverlight markup to create media and graphics, and manipulate them with dynamic languages and managed code. Silverlight also enables you to use professional-quality tools like Visual Studio for coding and Microsoft Expression Blend for layout and graphic design.

Reference by :http://msdn.microsoft.com