WordPress at a glance
action is not described

wp_unregister_sidebar_widget action-hook . WP 3.0.0

Fires just before a widget is removed from a sidebar.

Usage

add_action( 'wp_unregister_sidebar_widget', 'action_function_name_9605' );
function action_function_name_9605( $id ){
	// action...
}
$id(int)
The widget ID.

Where the hook is called

wp_unregister_sidebar_widget()
wp-includes/widgets.php 444
do_action( 'wp_unregister_sidebar_widget', $id );

Where the hook is used (in WP core)

Does not used.