For posts (category)
| get_object_taxonomies() | Return the names or objects of the taxonomies which are registered for the requested object or object type, such as a post object or post type name. |
| get_objects_in_term() | Retrieve object_ids of valid taxonomy and term. |
| get_the_category() | Retrieve post categories. |
| get_the_category_list() | Retrieve links to the categories to which the post belongs in either HTML list or custom format. |
| get_the_tag_list() | Retrieve the tags for a post formatted as a string. |
| get_the_tags() | Retrieve an array of post tags. Each array element is a WP_Term object. Can be used within The Loop. |
| get_the_taxonomies() | Retrieve all taxonomies associated with a post. Gets an array of HTML links. |
| get_the_term_list() | Displays a list of links to taxonomy elements (e.g. tags) related to a specified post. |
| get_the_terms() | Gets the taxonomy elements (terms) that are attached to the specified post. |
| has_category() | Checks whether the current or specified post has at least one of the specified categories. |
| has_tag() | Checks if the current post has any of the given tags. A conditional tag. |
| has_term() | Check if the current post has any of given terms. |
| is_object_in_taxonomy() | Determine if the given object type is associated with the given taxonomy. |
| is_object_in_term() | Determine if the given object is associated with any of the given terms. |
| the_category() | Displays links to the categories to which the post belongs in either HTML list or custom format. |
| the_tags() | Retrieve the tags links for a post. |
| the_taxonomies() | Display the taxonomies of a post with available options. |
| wp_delete_object_term_relationships() | Will unlink the object from the taxonomy or taxonomies. |
| wp_get_object_terms() | Retrieves the terms associated with the given object(s), in the supplied taxonomies. |
| wp_get_post_categories() | Retrieve the list of categories for a post. |
| wp_get_post_tags() | Gets a list of tags for a specified post as an array. |
| wp_get_post_terms() | Gets the elements of the specified taxonomy (tag, category) to which specified post is associated. |
| wp_remove_object_terms() | Remove term(s) associated with a given object. |
| wp_set_object_terms() | Create Term and Taxonomy Relationships. |
| wp_set_post_categories() | Set categories for a post. |
| wp_set_post_tags() | Set the tags for a post. |
| wp_set_post_terms() | Sets the terms for specified post (sets categories for post). |