"A web widget is a small piece of interactive content (like an ad or a game) that can be dynamically embedded into a web page.

Widgets allow for a new level of expression and creativity as personal web publishers use them to create value and interest in their blogs, social networks, personal home pages, and web sites.

In addition, widgets give large-scale online services a greater reach and visibility into the off-domain consumption of their core web services across multiple platforms."  See also blidgets.

Source: widgetbox.com