A distribution of Drupal is a customized installation package that includes additional modules, themes, and/or other components beyond what is included in an official release of Drupal. They can contain:

• Third Party Components: Admin Menu/Toolbar, Webform, Redirect, etc.
• Custom Components: Things you write or have written for you by developers
• Custom Configuration: Pre-configure settings of built-in or add-on components
• Install Profile: A recipe listing any and all of the above to be enabled when Dupal is being installed.