Your website may contain several levels of Navigation Menus.
Your Main Menu, also called your Primary Navigation Menu, contains links that are sometimes called Parent Items. Website design best practices recommend no more than 6 Primary Navigation choices.
Some Main Menu items will open sub-menus. Your sub-menus may also be called your secondary navigation or sub-navigation menu.
Website design best practices recommend that there should be no more than 6-8 sub-menu choices under each main menu item.
You may also have 3rd tier navigation items on your site, which correspond to secondary navigation menu items. Website best practices recommend that there should be no more than 5-7 3rd tier navigation choices for any Secondary Navigation item.