WordPress/wp-includes/taxonomy.php

<?php
/**
 * Taxonomy API
 *
 * @since 2.3.0
 *
 * @package WordPress
 * @subpackage Taxonomy
 */

require_once( ABSPATH . WPINC . '/taxonomy-functions.php' );
require_once( ABSPATH . WPINC . '/class-wp-tax-query.php' );