In WordPress, a menu is an array of items arranged to make navigation through the website easier for visitors.
Menus can consist of links to posts, pages, categories, tags, custom post types, custom taxonomies, or custom links.
Menus can consist of top menus and nesting submenus.
They can be displayed in several locations on your WordPress website: in the website header and/or footer, depending on your theme, or in a widget.
How to Add a Menu in WordPress
To add a menu in WordPress, go to Appearance>Menus. You can also access menus from hovering over your website name from the front of the website, or from the customizer.
To learn more about how to create a menu, read this post.
A menu bar is a graphical control element which contains drop-down menus.
The menu bar's purpose is to supply a common housing for window- or application-specific menus which provide access to such functions as opening files, interacting with an application, or displaying help documentation or manuals. Menu bars are typically present in graphical user interfaces that display documents and representations of files in windows and windowing systems but menus can be used as well in command line interface programs like text editors or file managers where drop-down menu is activated with a shortcut or combination key.