Drupal Content Management System

Drupal is an open source modular framework and Content Management System (CMS) written in the programming language PHP. It is used as a "back end" system for many different types of Web sites, ranging from small personal blogs to large corporate and political sites.

The standard release of Drupal, known as "Drupal core", contains basic features common to most CMSs. These include the ability to register and maintain individual user accounts, administration menus, RSS-feeds, customizable layout, flexible account privileges, logging, a blogging system, an Internet forum, and options to create a classic "brochureware" Web site or an interactive community Web site.

Source: Wikipedia.org