What is Drupal?

Drupal is a Content Management System(CMS). It's an open source content and free CMS framework written in PHP. It enables you to organize, manage and publish content with ease and comes with a variety of customization option.

Drupal is free, open source software that can be used by individuals or groups of users  to easily create and manage many types of Web sites. The application includes a content management platform and a development framework.