WordPress Widgets are WordPress Plugins that add visitor visual and interactivity options and features, such as sidebar widgets for post categories, tag clouds, navigation, search, etc.

They were originally designed to provide a simple and easy-to-use way of giving design and structure control of the WordPress Theme to the user in the sidebar, which is now available on properly „widgetized“ WordPress Themes to include the header, footer, and elsewhere in the WordPress design and structure.