On occasion, you will find that the Hidden checkbox in the web part is grayed out. The option to hide web parts is effectively disabled in Enterprise Wiki pages, such as the pages found in the Site Pages library.
Although you can use SharePoint Designer to hide web parts on a Wiki page, there is an easier, less risky way of doing it. By adding the query string parameter “?toolpaneview=2” to the URL and reloading the page, a tool pane appears that allows you to add a web part of your choice to the “bottom” web part zone of Enterprise Wiki pages.
The Hidden checkbox is now re-enabled, allowing you to hide the web part. The only caveat is that if you wish to view the hidden web part or edit its properties you will have to reload the page with the “?toolpaneview=2” query string.