The "Submenu toggle" allows you to create a heading in your website menu, but there is no attached page or link. We may need this to group a bunch of pages together under a heading, but we don't want (or need) to build an extra page on the website for that menu point.
How to use:
Simply choose that option under the "More items" then in the menu list you will need to edit that new item, give it the name you would like, and then place it in the menu where you need it.