The multisite feature

Every Drupal codebase has a site’s directory. Single site instances leverage a sites/default directory to store the Drupal application settings, which includes its corresponding database. Another standard convention is to place custom and contributed modules within the sites/all directory. The intention for this convention is to potentially share code. The “default” site still has access to the code found in sites/all.

Default does not have to be the only site if used at all. Suppose a university wants to offer each department its website but wants to maintain all websites through centralized IT. One Drupal codebase could be leveraged that has a specific site directory for every department in the university. The same modules and features can then be installed on each site given they're all running the same code.

Each Drupal application has a sites.php file that helps map a domain to its corresponding site directory. This is not...