Drupal is a CMS system (Content Management System), which basically means that a developer can setup a web page and the client can maintain the contents by themeselves in a simple way.

Compared to other CMS systems Drupal has a lot of facilities and can be "tweaked" to:

• Present almost all kinds of information like text, multimedia, structured data etc.
• Create interactive pages where the user can contribute contents by forums, article writing, polls, questionnaire etc.
• Handle many user roles (depending on permission) and render pages dependent on who is logged in

More facilities also means steeper learning curves and even though Drupal has improved immensely regarding developer experience during the last versions, Drupal is still considered one of the CMS systems that requires expert knowledge for the developer - NOT for the daily content provider or user.