我终于解决了这个问题。我之所以复制代码，是因为它可能会帮助某些人：）我通过填充arrray并检查品牌是否存在，找到了解决方案，因此我只获得每个品牌一次。

   <?php

    //Query to match department
    $args = array(
     \'tax_query\' => array(
         array(
             \'taxonomy\' => \'department\',
             \'field\' => \'slug\',
             \'terms\' => array( \'department_name\' )
         ),
     ),
     \'orderby\' => \'title\',
     \'order\' => \'ASC\',
     \'post_type\' => \'prod\', \'posts_per_page\' => \'-1\', \'posts_per_page\' => \'-1\'
    );
    $query = new WP_Query( $args );

    if ( $query->have_posts() ) {

      // Array of brands
      $brands= array();

      $term = $query->queried_object;

     while ( $query->have_posts() ) : $query->the_post(); ?>
         <!-- Loop to show the brand -->
         <?php
          $terms = get_the_terms( $post->ID , \'brabds\' );
 // Loop por el array de marcas
          if ( $terms != null ){
            foreach( $terms as $term ) {

              // I want to check if my brand has only one product or more
              // Only one product
              if ($term ->count == 1){
                // I create a variable so I can check if it\'s in my brands array
                   $marca = $term->name;
                // If is not in array, push it there
                    if ( ! in_array($marca, $marcas)){
                        array_push($marcas, $marca);
                // This query is to link to a product and get some info
                        $tax_query = \'\';
                                    $tax_query[] = array(\'taxonomy\' => \'brands\',\'field\' => \'term_id\',\'terms\' => $term->term_id);
                                    $term_post = get_posts(array(\'post_type\' => \'prod\',\'tax_query\' => $tax_query));
                                    if (!empty($term_post)) {
                                        $term_post_link = get_permalink($term_post[0]->ID);
                                        $id_prod = url_to_postid($term_post_link);
                                        $nombre_prod = get_the_title($term_post[0]->ID);
                                        echo \'<a title="\'.$term->name.\'" rel="\'.$id_prod.\'">\'.$term->name.\'</a>\';
                                    }
                    }
              }
              // Marcas MULTI
              else{
                // If there are more than a product, do the same thing but query as my needs
                    $marca = $term->name;                    
                    if ( ! in_array($marca, $marcas)){
                        array_push($marcas, $marca);
                        echo \'<a rel="\'.$term->term_id.\'" title="\'.$term->name.\'">\'.$term->name.\'</a>\';
                    }
              }
            }
          }
          // End loop
?>

    <?php
    endwhile;

    wp_reset_query();
    } ?>