The document discusses the evolution of fields and the field API in Drupal from Drupal 6 to Drupal 7. In Drupal 6, fields were tied to nodes via the Content Construction Kit (CCK) module, but in Drupal 7, the Field API allows any entity like nodes, users, and comments to use fields. The Field API in Drupal 7 includes modules for attaching fields to entities, field types, CRUD operations, and storage. It provides APIs for core and contrib modules to integrate fields in a standardized way.