uh... and what is ur interest in widgets specifically? as far as i'm aware, the term doesnt even refer to just one thing. It's just like saying "appliance", vs saying "microwave", or "vacuum cleaner".. What's the context in which this term is used?
Widgets are generally used for cross site information sharing, and are made up of javascript and any of the server side scripting language. For example, a weather information site can create a weather information widget which i can put on my site to display current weather information of my city.