WordPress at a glance
action is not described

admin_bar_menu action-hook . WP 3.1.0

Load all necessary admin bar items.

This is the hook used to add, remove, or manipulate admin bar items.

Usage

add_action( 'admin_bar_menu', 'action_function_name_2401' );
function action_function_name_2401( $wp_admin_bar ){
	// action...
}
$wp_admin_bar(WP_Admin_Bar)
WP_Admin_Bar instance, passed by reference

Where the hook is called

wp_admin_bar_render()
wp-includes/admin-bar.php 83
do_action_ref_array( 'admin_bar_menu', array( &$wp_admin_bar ) );

Where the hook is used (in WP core)

wp-includes/class-wp-admin-bar.php 575
add_action( 'admin_bar_menu', 'wp_admin_bar_my_account_menu', 0 );
wp-includes/class-wp-admin-bar.php 576
add_action( 'admin_bar_menu', 'wp_admin_bar_search_menu', 4 );
wp-includes/class-wp-admin-bar.php 577
add_action( 'admin_bar_menu', 'wp_admin_bar_my_account_item', 7 );
wp-includes/class-wp-admin-bar.php 580
add_action( 'admin_bar_menu', 'wp_admin_bar_sidebar_toggle', 0 );
wp-includes/class-wp-admin-bar.php 581
add_action( 'admin_bar_menu', 'wp_admin_bar_wp_menu', 10 );
wp-includes/class-wp-admin-bar.php 582
add_action( 'admin_bar_menu', 'wp_admin_bar_my_sites_menu', 20 );
wp-includes/class-wp-admin-bar.php 583
add_action( 'admin_bar_menu', 'wp_admin_bar_site_menu', 30 );
wp-includes/class-wp-admin-bar.php 584
add_action( 'admin_bar_menu', 'wp_admin_bar_customize_menu', 40 );
wp-includes/class-wp-admin-bar.php 585
add_action( 'admin_bar_menu', 'wp_admin_bar_updates_menu', 50 );
wp-includes/class-wp-admin-bar.php 589
add_action( 'admin_bar_menu', 'wp_admin_bar_comments_menu', 60 );
wp-includes/class-wp-admin-bar.php 590
add_action( 'admin_bar_menu', 'wp_admin_bar_new_content_menu', 70 );
wp-includes/class-wp-admin-bar.php 592
add_action( 'admin_bar_menu', 'wp_admin_bar_edit_menu', 80 );
wp-includes/class-wp-admin-bar.php 594
add_action( 'admin_bar_menu', 'wp_admin_bar_add_secondary_groups', 200 );