What is silverlight?

• Silverlight is a web browser plug-in.
• Plug-in is small in size and self-in self-contained.It can be installed on demand.
• Plug-in runs in all popular browsers, including Microsoft Internet Explorer, Mozilla Firefox, Apple Safari, Opera.
• Silverlight is a plug-in similar to Flash in a sense. It won't run and use any machine resources until you hit a Page that contains Silverlight application.
• Pug-in runs cross-browser , cross-platform that exposes a programming framework and features that are a subset of the .NET Framework and Windows Presentation Foundation (WPF)
• Silverlight is a powerful development platform for creating rich media applications and business applications for the Web, desktop, and mobile devices 

Silverlight and Flash

• Silverlight is more of a presentation tool. If Flash is the content, Silverlight is the container and the mode of delivery.
• Silverlight goes beyond Flash, as it offers more features for delivering rich web content as a single package rather than a conglomeration of different content delivery methods.
• Silverlight tries to combine the creative delivery of Flash with the application development.
• Silverlight applications are delivered to a browser in a text-based markup language called XAML. XAML is a declarative markup language that you can use to define the UI elements for your Silverlight-based application. Search engines, like Google, can scan XAML but they can't dive into compiled Flash applications. So Silverlight applications are more findable.