Internal events are referred as hooks, because when one of the events occurs, Drupal allows modules to hook into the path of execution at that point.
Drupal’s built-in trigger module allows you to associate some action with a certain event. In the code, an event is defined as a unique hook-operation combination.
- Event: This term is generally understood as a message sent from one component of a system to other components.
- Hook: This programming technique allows modules to “hook into” the flow of execution.
- Operation: This refers to the specific process that is being performed within a hook.
- Trigger: This refers to a specific combination of a hook and an operation with which one or more actions can be associated. For example, the action of beeping can be associated with the login operation of the user hook.
An action is something that Drupal does. They are functions that Drupal can introspect and loosely couple with events.