Define functions that alter the behavior of Drupal core.
One way for modules to alter the core behavior of Drupal (or another module) is to use hooks. Hooks are specially-named functions that a module defines (this is known as "implementing the hook"), which are discovered and called at specific times to alter or add to the base behavior or data (this is known as "invoking the hook"). Each hook has a name (example: hook_batch_alter()), a defined set of parameters, and a defined return value. Yo