The Trigger module provides the ability to take a particular action when a trigger occurs.
Actions include functional tasks that are defined by Drupal core modules, and advanced actions that can be defined by the system administrator. Contributed modules can introduce new actions. Some examples of actions are sending an email, publishing a node, banning a user or promoting a node to the front page of a website.
Triggers are defined by modules, and typically result from some characteristic change in an entity maintained by that module. Some examples of triggers are: deleting content, adding a comment, a user has logged in, or adding a term. In addition to the triggers provided by Drupal core modules, more triggers may be added by installed contributed modules.
The Trigger module allows you to perform useful tasks by associating actions with specific triggers, such as e-mailing an administrator (the action) when a user account is deleted (the trigger), or automatically unpublishing a comment (the action) if the added comment (the trigger) contains certain words. The Trigger module is included in the core Drupal installation. The module must be enabled to use it.