The acronym "CCK" comes from Drupal and stands for "Content Construction Kit".
A CCK allows you to expand the information you add to your site, beyond simply a title and body field.
In this presentation, Jon Neubauer introduces you to all of the popular Joomla CCK solutions. Jon looks at K2, ZOO and Seblod.
If your website has complex content requirements, you'll want to watch Jon's talk: