Drupal is the English pronunciation for the Dutch word 'druppel' which means 'drop'.
While it is basically a SlashClone it has adopted a premise that "everything should be a node" which allows it to implement new features quite easily. You'll find modules for Drupal which do everything from currency conversion and photo galleries to mail list and CVS integration.
Credits
The article is originally based on materials from infoAnarchy wiki and is updated as needed.