1. Drush is a command line shell and scripting interface for Drupal. It provides commands to install, update, and manage Drupal sites.
2. Drush comes with core commands for cache clearing, module enabling/disabling, and more. Additional commands are available through extensions like Devel, Backup and Migrate, and Drush Make.
3. The document provides examples of how Drush can help streamline the Drupal development process, such as downloading a site, enabling modules, and generating a custom module.