WordPress at a glance
action is not described

woocommerce_checkout_shipping action-hook . WC 1.0

Usage

add_action( 'woocommerce_checkout_shipping', 'action_function_name_2901' );
function action_function_name_2901(){
	// action...
}

Where the hook is called

In file: /templates/checkout/form-checkout.php
woocommerce_checkout_shipping
woocommerce/templates/checkout/form-checkout.php 44
<?php do_action( 'woocommerce_checkout_shipping' ); ?>

Where in WP core the hook is used WooCommerce

woocommerce/includes/class-wc-checkout.php 59
add_action( 'woocommerce_checkout_shipping', array( self::$instance, 'checkout_form_shipping' ) );