What is an additional list of menu options that appears when one of the menu items is selected?

An additional list of menu options that appears when one of the menu items is selected is often referred to as a "sub-menu" or "dropdown menu." This feature allows users to access more specific choices related to the selected item, enhancing navigation and providing a more organized structure. Sub-menus can be particularly useful in applications and websites to categorize options and streamline user experience.