Index: wp-includes/taxonomy.php
===================================================================
--- wp-includes/taxonomy.php	(revision 24811)
+++ wp-includes/taxonomy.php	(working copy)
@@ -300,6 +300,8 @@
  *
  * labels - An array of labels for this taxonomy. You can see accepted values in {@link get_taxonomy_labels()}. By default tag labels are used for non-hierarchical types and category labels for hierarchical ones.
  *
+ * description - A short descriptive summary of what the taxonomy is for. Defaults to blank.
+ *
  * @package WordPress
  * @subpackage Taxonomy
  * @since 2.3.0
@@ -329,6 +331,7 @@
 		'labels' => array(),
 		'capabilities' => array(),
 		'show_in_nav_menus' => null,
+		'description' => ''
 	);
 	$args = wp_parse_args($args, $defaults);