Drush is a command line interface for Drupal. Most of the tasks for building and maintaining a website are repetitive and involve filling in forms on administration pages. The majority of these tasks can be achieved with a single Drush command, drastically shortening the development and maintenance time of a project.
Drupal developers or themers who have already built a few Drupal sites and understand its web-based administration.
If you have not ever touched a terminal, this book is progressively paced starting with the structure of a command, and finishing with how to simplify complex commands that interact with remote servers. However, you should learn the basic terminal commands in order to move around, copy and manage directories, connect and interact with a database, log in to remote systems, and have basic PHP programming skills.