Microsoft Silverlight is a web application framework that allows for rich multimedia and interactive experiences on the web. It provides graphics, animations, and interactivity similar to Adobe Flash. Silverlight uses XAML for user interfaces and a subset of the .NET Framework for programming. Key features include smooth streaming, pixel shader effects, out-of-browser applications, 3D graphics, and support for additional features in later versions like webcams and printing. While it requires a plugin, Silverlight enables rich interactive applications for the web.