WordPress at a glance
filter is not described

woocommerce_(type)fields filter-hook . WC 1.0

Important note on this filter: Changes to address fields can and will be overridden by the woocommerce_default_address_fields. The locales/default locales apply on top based on country selection. If you want to change things like the required status of an address field, filter woocommerce_default_address_fields instead.

Usage

add_filter( 'woocommerce_(type)fields', 'filter_function_name_7706', 10, 2 );
function filter_function_name_7706( $address_fields, $country ){
	// filter...

	return $address_fields;
}
$address_fields
-
$country
-

Where the hook is called

WC_Countries::get_address_fields()
woocommerce_(type)fields
woocommerce/includes/class-wc-countries.php 1514
$address_fields = apply_filters( 'woocommerce_' . $type . 'fields', $address_fields, $country );

Where in WP core the hook is used WooCommerce

woocommerce/packages/woocommerce-admin/src/Features/ActivityPanels.php 36
add_filter( 'woocommerce_admin_get_user_data_fields', array( $this, 'add_user_data_fields' ) );
woocommerce/packages/woocommerce-admin/src/Features/Analytics.php 43
add_filter( 'woocommerce_admin_get_user_data_fields', array( $this, 'add_user_data_fields' ) );
woocommerce/packages/woocommerce-admin/src/Features/AnalyticsDashboard.php 42
add_filter( 'woocommerce_admin_get_user_data_fields', array( $this, 'add_user_data_fields' ) );
woocommerce/packages/woocommerce-admin/src/Features/Homescreen.php 41
add_filter( 'woocommerce_admin_get_user_data_fields', array( $this, 'add_user_data_fields' ) );
woocommerce/packages/woocommerce-admin/src/Features/MobileAppBanner.php 32
add_filter( 'woocommerce_admin_get_user_data_fields', array( $this, 'add_user_data_fields' ) );