Question about nodereference_elements function

function nodereference_elements() {
  return array(
    'nodereference_select' => array(
      '#input' => TRUE,
      '#columns' => array('uid'), '#delta' => 0,
      '#process' => array('nodereference_select_process'),
      ),
    'nodereference_autocomplete' => array(
      '#input' => TRUE,
      '#columns' => array('name'), '#delta' => 0,
      '#process' => array('nodereference_autocomplete_process'),
      '#autocomplete_path' => FALSE,
      ),
    );
}

Can someone explain to me what 'name' and 'uid' refer to and why the nodereference module needs to use these words in this function? And why would select lists need one and autocomplete need the other? Why does it never refer to 'nid' here, which is the actual field it is creating?