Nelit said..
Widgets, also known as gadgets, are small, reusable components that allow content from multiple sources to be easily integrated without programming. Many of the largest online and operating system vendors, including Google, Yahoo!, Microsoft, and Apple, support their own, incompatible form of widgets.
The widgets are often part of user-configurable home pages or dashboards (although many types can be included in any web page). These easily-pluggable widgets extend the reach of content and ecommerce providers, social networks, and others by giving users a simple way to build on their data and services.