Widgets are tools that you can add to your site to customize it and/or allow for additional features. There are a number of them available through U.OSU and this help article will show you how to activate them.
Some plugins include additional widgets. For example, the Jetpack plugin contains a number of widgets that you can activate: Sharing, Slideshows, Title Galleries, Widget Visibility and more. The Jetpack widgets help you display your content; however, the plugin allows you to create them.