Drupal is a open-source content management framework written in PHP and distributed under the GNU General Public License. It is used as a back-end framework for at least 2.1% of all websites worldwide ranging from personal blogs to corporate, political, and government sites including whitehouse.gov and data.gov.uk. It is also used for knowledge management and business collaboration.
The standard release of Drupal, known as Drupal core, contains basic features common to content management systems. These include user account registration and maintenance, menu management, RSS feeds, page layout customization, and system administration. The Drupal core installation can be used as a simple website, a single- or multi-user blog, an Internet forum, or a community website providing for user-generated content.
As of August 2013, there are more than 22,900 free community-contributed addons, known as contributed modules, available to alter and extend Drupal's core capabilities and add new features or customize Drupal's behavior and appearance. Because of this plug-in extensibility and modular design, "The Drupal Overview" on Drupal's website describes it as a content management framework. Drupal is also described as a web application framework, as it meets the generally accepted feature requirements for such frameworks.