drupal_alter
http://api.drupal.org/api/drupal/includes%21module.inc/function/drupal_alter/7
Special function to create a hook of type hook_hooktype_alter

module_invoke
http://api.drupal.org/api/drupal/includes!module.inc/function/module_invoke/7
Fonction principale qui permet de créer un hook dans drupal. Il appelle les modules passés en arguments module_invoke_all('entity_view', $asset, 'asset', $view_mode); In this exemple hook_entity_view will be called, with ther arguments $assets, 'asset', $view_mode If we want to implement it we need to write a function called
function mymodule_entity_view($asset, 'asset', $view_mode);

module_implement
http://api.drupal.org/api/drupal/includes!module.inc/function/module_implements/7
Retourne un array de modules qui implemente un hook donné