What's meaning of %contact in this menu path? $items['admin/structure/contact/edit/%contact'] = array(
    'title' =&gt; 'Edit contact category',
    'page callback' =&gt; 'drupal_get_form',
    'page arguments' =&gt; array('contact_category_edit_form', 4),
    'access arguments' =&gt; array('administer contact forms'),
    'file' =&gt; 'contact.admin.inc',
);


How does it get the path admin/structure/contact/edit/%contact and what does it mean by %contact?
All requests on admin/structure/contact/edit/[anything] will be handled by a Drupal form callback, contact_category_edit_form() in contact.admin.in` which returns a form array.

%contact means this parameter will be passed to contact_load() and the result will be pass to contact_category_edit_form() as first argument.

See hook_menu().


  Registered paths may also contain special "auto-loader" wildcard components in the form of '%mymodule_abc', where the '%' part means that this path component is a wildcard, and the 'mymodule_abc' part defines the prefix for a load function, which here would be named
  mymodule_abc_load().