Microsoft Silverlight (or simply Silverlight) is a deprecated application framework for writing and running rich Internet applications, similar to Adobe Flash. A plugin for Silverlight is still available for some browsers. While early versions of Silverlight focused on streaming media, later versions supported multimedia, graphics, and animation, and gave support to developers for CLI languages and development tools. Silverlight was also one of the two application development platforms for Windows Phone, but web pages using Silverlight did not run on the Windows Phone or Windows Mobile versions of Internet Explorer, as there was no Silverlight plugin for Internet Explorer on those platforms.
Microsoft plans to terminate support for Silverlight on Internet Explorer 11 on October 12, 2021, the last remaining web browser still supporting Silverlight.
With all of that said and done, Microsoft Silverlight is generally considered to be a failure. It was released way too late.