Silverlight is a Web application framework developed by Microsoft. To view videos in Microsoft Website and websites developed with Silverlight, you must have Silverlight installed in your computer.
Silverlight runs in all popular browsers like Internet Explorer, Firefox, Opera, Chrome and Safari. As to view rich media content websites with flash content you need to have flash plug-in installed, like that to view websites with Silverlight you must have Silverlight plug-in installed in your browsers.
Though you can install this online from Microsoft website, it is highly encouraged to have offline installer for silverlight to install it on multiple computers offline.
Download Silverlight offline installer from any of the links given below.