Implementing callback function in hook_menu() In the link given below ,
https://drupal.org/node/224333
So as given in below statement you do not have to declare the callback path* what does this mean?
I have hook_menu() in d6 which is as follows : 

$items['ort/add/ion'] = array(
    'type' =&gt; MENU_CALLBACK,
    'page callback' =&gt; 'ort_add_ion',
    'access arguments' =&gt; array('access content'),
    'file' =&gt; 'ort.tion.inc',
  );


Does the link say that for d7 you do not need page callback or something different?


In Drupal 7, you do not have to declare the callback path in hook_menu(), and the callback function is far simpler.

Drupal 6:

&lt;?php
// This function must be pointed to in hook_menu() in D6.
function my_callback_function() {
  // ... Much work to build the form ....

  drupal_process_form($form_id, $form, $form_state);
  $form = drupal_rebuild_form($form_id, $form_state, $args, $form_build_id);

  $output = drupal_render($form);

  // Final rendering callback.
  print drupal_json(array('status' =&gt; TRUE, 'data' =&gt; $output));
  exit();
}
?&gt;


Drupal 7:

&lt;?php
// No path needs be set up to point to the function, and $form and $form_state are provided.
function my_callback_function($form, &amp;$form_state) {
  // Often you would select a portion of the form to match #ajax['wrapper']
  // rather than processing the whole form.
  return $form;  // Either HTML or a render array may be returned.
}
?&gt;
The simple answer is it is for ajax items. In drupal 6 you had to declare a path and direct your ahah to it with ['#ahah']['path']. In drupal 7 it is handled automatically and you now use ['#ajax']['callback'] to call the function without having to declare a path.