Views is a way to make custom lists of content and other data in Drupal. It is incredibly flexible and can list teasers, full nodes, specific fields from CCK nodes, users, taxonomy, and much more. Views can create full pages, blocks, integrate into Panels and many other modules. Views just underwent a complete rewrite to solidify it for the foreseeable future (Drupal 6 and beyond). Views is targeted for eventual inclusion in Drupal core. As with CCK, this is one of the most important modules in Drupal, and will never fail to be supported.