I have a hierarchy of pages in Wordpress, what does this hierarchy mean? Since I also have a hierarchy of menu items which shows the menu. Whats the difference and why do they both have a hierarchy?
It's how they are stored in the database. It depends on your theme's & plugins about how they want to use this hierarchy but typically-
The hierarchy of menus will be reflected on the navigation menus.
The hierarchy of pages will be reflected on things such as breadcrumbs.