WordPress at a glance
action is not described

shutdown action-hook . WP 1.2.0

Fires just before PHP shuts down execution.

Usage

add_action( 'shutdown', 'action_function_name_3123' );
function action_function_name_3123(){
	// action...
}

Changelog

Since 1.2.0 Introduced.

Where the hook is called

shutdown_action_hook()
shutdown
wp-includes/load.php 954
do_action( 'shutdown' );

Where the hook is used (in WP core)

wp-includes/default-filters.php 352
add_action( 'shutdown', 'wp_ob_end_flush_all', 1 );