Example implementation of Drupal 7 hook_permission

hook_permission.php

<?php
/**
 * Implements hook_permission().
 *
 * Defines a new permission called 'my custom permission'.
 */
function my_custom_module_permission() {
  return array(
    'my custom permission' => array(
      'title' => t('My custom permission'),
      'description' => t('Allows users to perform a task in my module.'),
    ),
  );
}