Drupal 7 introduced many new APIs, most notably the Field API. The Field API is a powerful but complex system that defines the structure and behavior of fields. It introduces several new concepts including bundles, field storage, field types, widgets, and formatters. Fields describe the data structure and behavior, while instances store widget and formatter settings and are easier to update. The Field API provides functions to attach, load, and update fields on entities. It handles fields already attached rather than the attachment process itself. Taxonomy terms are also now full entities with their own API.