Microsoft™ Silverlight is a development framework that can be used for creating visually stunning media experiences for the web. It can be used across multiple browsers and also across various platforms. As it is part of the .NET framework, it has a powerful collection of libraries that help in creating wonderful, interactive experiences for the user. Microsoft™ launched Silverlight as a direct competition to Adobe™ Flash. They both provide similar features and functionality but the advantage with Silverlight is that it is built as a part of the .NET Framework.
Silverlight uses XAML (Extensible Application Markup Language) to describe visual user interfaces, and is a subset of the WPF (Windows Presentation Foundation). WPF is basically the graphics component of the .NET Framework and helps in developing rich user interfaces for .NET applications.