Drupal is an open source content management system (CMS) written in PHP. It allows users to build and manage websites through a user interface without having to manually code and edit HTML files. Drupal has a modular architecture that can be extended through modules and themes to add functionality and customize appearance. It uses a database to store content, users, and site configurations. Content in Drupal is primarily managed through nodes, which are content objects that can be customized into different content types like pages or blog posts. Drupal provides role-based access control and permissions to manage user access. Popular modules extend its functionality for features like user management, content types, menus, views, and more.