The Content Construction Kit is a Drupal module that allows users to add custom fields to content types.
The Content Construction Kit (CCK) is a collection of Drupal modules that can be used to create content types whose nodes follow a defined structure beyond that of a title and a body.
The CCK provides field types and widgets. The user (usually an administrator or developer) adds a field to a content type by selecting a field type, a widget and a name for the field. When a user creates a node of that content type, the widget is displayed and the user can enter data into it according to the field type. This data is saved together with the node that gets created and displayed when the node is displayed.
The CCK provides field types for (amongst others) text, numbers, nodes, users. Widgets for (amongst others) line input, text areas, select lists, radio buttons, checkboxes are available. Additional field types and widgets can be created by developers and some are available as extension modules on drupal.org.
CCK fields are automatically exposed to the Views module.