Definition:
The Mac OS X menu bar is a thin horizontal bar that is permanently anchored to the top of the desktop. The menu bar always contains the Apple menu (identified by an Apple logo icon), as well as the basic File, Edit, View, Windows, and Help menu items. Currently active applications may add their own menu items to the menu bar.
The far right side of the menu bar has an area reserved for menu extras. This area of the menu bar can display optional menus for controlling applications and configuring the system. Common menu extras include the date and time, a volume control, and Spotlight, a Mac OS X search tool.
Examples:
Metro, a weather application, adds a menu extra to the menu bar, for quick access to local weather information.
