WordPress at a glance
action is not described

woocommerce_helper_output action-hook . WC 1.0

Usage

add_action( 'woocommerce_helper_output', 'action_function_name_2999' );
function action_function_name_2999(){
	// action...
}

Where the hook is called

WC_Admin_Addons::output()
woocommerce_helper_output
woocommerce/includes/admin/class-wc-admin-addons.php 634
do_action( 'woocommerce_helper_output' );

Where in WP core the hook is used WooCommerce

woocommerce/includes/admin/helper/class-wc-helper.php 45
add_action( 'woocommerce_helper_output', array( __CLASS__, 'render_helper_output' ) );