Microsoft Silverlight is a web application framework that allows developers to create rich interactive applications and media experiences for the web. It uses XAML as its user interface definition language and supports .NET languages like C# for programming logic. Silverlight applications run in the browser in a sandboxed environment. It has gone through multiple releases that have expanded its capabilities like supporting .NET languages fully, enabling out of browser applications, and improving tools for developers. It provides an alternative to Flash and aims to deliver a consistent cross-browser experience.