php - What does it mean to have 3 brackets after array? -

i curious args['fields'][$k]['order'] means. new php , far know args['fields'] mean user talking value key 'fields' in array args. mean have 3 brackets (all containing something) after args part?

foreach($this->args['fields'] $k => $field){             if(!isset($field['order']))                 $this->args['fields'][$k]['order'] = 10; 

this means args 3 dimensional array. key 'fields' in args points array. key $k in array points array. key 'order' in array being assigned value 10.