It shows the html (web) content that is configured in the Web Panel item in the browser of the viewer interface. This can be a simple text to an official web page, depending on the type of panel; Text, Web or Excel.
The panel currently has a set width and height, which is configured in the Web Panel's panel, though the actual size of the panel is still limited by the size of your window.
Web panel showing the content of a Text Panel item.
Web panel showing the content of a Web Panel item.
Web panel showing the content of an Excel Panel item.