There is only one menu bar, so the application menus displayed are those of the application that is currently focused. In Mac OS 8.5 and later, the menu can be dragged downwards, which would cause it to be represented on screen as a floating palette.

In the Classic Mac OS (versions 7 through 9), the right side contains the application menu, allowing the user to switch between open applications. If an icon is dragged and dropped vertically it will disappear with a puff of smoke, much like the icons in the dock. All of these menu extras can be moved horizontally by command-clicking and dragging left or right. On the right side, it contains menu extras (for example the system clock, volume control, and the Fast user switching menu (if enabled) and the Spotlight icon. In macOS, the left side contains the Apple menu, the Application menu (its name will match the name of the current application) and the currently focused application's menus (e.g. In the Macintosh operating systems, the menu bar is a horizontal 'bar' anchored to the top of the screen.