A WordPress Widget is a small block that performs a specific function. You can add these widgets in sidebars also known as widget-ready areas on your web page.
WordPress widgets were originally created to provide a simple and easy-to-use way of giving design and structure control of the WordPress theme to the user. Widgets can be easily
dragged and dropped into a specific widget area. You can find the list of available widgets and widget areas by going to the Appearance » Widgets section in your WordPress dashboard.
Widgets in WordPress allow you to add content and features in the widgetized areas of your theme which is mostly the sidebar. However these widget-ready areas can be in the
header, footer, sidebar, below content, and basically any other area in your theme. The available widget areas that you have in your theme will vary from theme to theme.