Drupal is a open source CMF (Content Management Framework), build in PHP
Follow out the documentation on Drupal.org to better understand the framework.
Drupal is a free and open-source content-management framework that can be tailored and customized to simple websites or complex web applications. Drupal grows as you grow with thousands of free modules and themes that will help you attract the web audience you need to deliver your message, grow brand awareness, and build your community.
Drupal is accessible and multilingual. The latest release of Drupal is the most powerful and accessible version of Drupal to date. With accessibility and multilingual capabilities built into Drupal, you can be assured that you'll have the capability to reach the audience that you are targeting to convey your message.
Drupal is flexible by design. From desktop applications such as Aquia Dev Desktop that allows you to build your web application on your own computer, or hosting from a Drupal hosting provider, you can be sure that your Drupal website and/or application will run on the platform that meets your needs. Drupal is easy to move and scale. Drupal conforms to your needs.