Taxonomy is the system WordPress uses to group and categorize content, allowing editors to organize posts, pages, and custom post types into logical collections that power archive pages, filtering, sitemaps, and internal navigation. WordPress ships with two built-in taxonomies: Categories (hierarchical — they can have parent-child relationships, like folders) and Tags (flat and freeform, applied as keywords). Developers can register custom taxonomies for any content type using register_taxonomy(), specifying whether it is hierarchical, which post types it applies to, and whether it should expose a REST API endpoint. For example, a recipe site might register a "Cuisine" taxonomy applied to a "Recipe" custom post type. Each taxonomy term generates its own archive URL, and WordPress exposes term data as WP_Term objects with an ID, name, slug, description, and parent ID.
Glossary entry
