Drupal is an open-source content management system (CMS) used for building websites and web applications. It is one of the most popular CMS platforms, with a large community of developers and users contributing to its development and maintenance. Drupal is known for its flexibility, scalability, and security features, making it a popular choice for enterprise-level websites, government websites, and high-traffic websites. Its modular architecture allows users to add and customize features easily, and its extensive library of modules and themes make it a versatile platform for creating unique and engaging online experiences.