Drupal is a open source CMS (Content Management System) for websites. Drupal enables webmasters to create professional websites with a minimal amount of specialized coding or systems support.
Drupal's architecture consists of a core platform that can be customized with user-supplied profiles, modules, themes, and languages. Drupal separates content from presentation, and -- when combined with Drupal's "codeless" module building -- allows high flexibility, while maintaining relative simplicity. This yields high productivity in designing and deploying a wide variety of websites, thus driving Drupal's wide user base.
Code (when required) is written in PHP and the content is stored in a MySQL database. In general, Drupal is fairly approachable for someone with basic programming and web authoring skills. It is a generally low-overhead solution for web page construction that enables multiple contributors. Many university departments support Drupal for their investigators and will help with Drupal administration.