Use it for questions about the engine which allows site administrators to automate actions: the Rules module.
Rules is an engine that allows site administrators to automate actions to be conditionally executed, either programmatically or in response to predetermined events.
Rules can react to Rules Events occurring on a Drupal site, such as a user logging in or a node being submitted. And it can perform customized follow-up Rules Actions such as redirecting to a certain page or setting field values which are to be conditionally executed if some Rules Conditions are satisfied.
Rules is also a framework used by other modules, allowing them to expose user-reconfigurable Rules Components with sets of Rules Actions and/or Rules Conditions that are managed in easy to import/export configuration files. Rules leverages the Entity API module to read and act on data and to work seamlessly with all types of variables and entities.