Flash is an Adobe product, introduced in 1996, which is classed as multimedia platform. It’s most commonly known for its use in animations on webpages, particularly those which allow the user to interact with the animation, for example clicking on one of a selection of options.
Technically Flash content can be created as a standalone file which users view with a dedicated program. However, it’s usually used by being embedded in a web page and played automatically by a plug-in for the browser.
Silverlight, which debuted in 2007 is Microsoft’s take on the multimedia plug-in. It’s main selling point is that it allows Windows Media format audio and video content to play on machines which don’t have Windows Media Player installed. As Silverlight is a much smaller download, it may be appealing to website visitors who wouldn’t bother downloading Windows Media Player just to watch a particular clip.