A Drupal 7 module is an extension for Drupal that either adds new functionality to your site or enhances current features. There are many modules included by default when you install Drupal 7, but not all of them are enabled by default.
In addition to the modules installed by default with Drupal 7, there are literally thousands of other modules available for Dupal 7, and you can find them on the Download and Extend portion of drupal.org.
In the next few tutorials, we’ll show you how to install and keep your modules up to date.