The EntityFieldQuery is not limited to node, it can be used to retrieve any entity types in Drupal 7. Here comes an example about getting taxonomy terms with EntityFieldQuery.

I would like to retrieve all terms with of a specific vocabulary which has vid = 1 with the descending weight order.

$query = new EntityFieldQuery;
$query->entityCondition('entity_type', 'taxonomy_term')
  ->propertyCondition('vid', 1)
  ->propertyOrderBy('weight');
 
$terms = $query->execute();

Done =)

Reference: Drupal’s EntityFieldQuery and Taxonomy
http://blog.rapiddg.com/2012/02/drupals-entityfieldquery-and-taxonomy/