Drupal multi-sites

On the server end, you can configure Drupal so that multiple sites can run using the same code base (i.e. referencing the same Drupal core, module, theme, and library code). Because there’s only one copy of the code that all the sites use, it reduces the number of updates you have to do to maintain the sites. In contrast, if you were to run each site independently, you would need to apply every Drupal core and module update to each site’s code base.