drush is a command line shell and scripting interface for Drupal, a veritable Swiss Army knife designed to make life easier for those of us who spend some of our working hours hacking away at the command prompt.
See http://drush.ws, the homepage for the drush project. It contains many important resources for drush users.
[A list of modules that include Drush integration.][3]
(drush is not a module)
[3]: http://A list of modules that include Drush integration.
