For posts (category)

get_object_taxonomies()

Gets the taxonomies related to the specified post type or the passed object.

get_objects_in_term()

Gets the IDs of objects (usually posts) that relate to the specified element of the specified taxonomy.

get_the_category()

Gets an array of categories data related to current post.

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()

Gets the HTML string of tags for the current post. The name of each tag will be a link to the archive of posts with that tag. Used in a loop.

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()

Checks if the specified post is associated with the specified taxonomy terms.

is_object_in_taxonomy()

Checks if the specified post type is associated with the specified taxonomy.

is_object_in_term()

Defines whether the specified object is associated with any of the specified taxonomy elements (term). Specific term(s) can be provided to check the association.

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 links to taxonomy terms of the current post. Used inside WordPress loop

wp_delete_object_term_relationships()

Destroys all relationships of the object (post, page) with the specified taxonomy(ies).

wp_get_object_terms()

Gets the terms (taxonomy elements) related to the given object(s) (posts) in the specified taxonomy.

wp_get_post_categories()

Gets the list of post categories as an array.

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()

Breaks the connection between the specified object and the specified term, i.e., removes the post from the taxonomy element (category).

wp_set_object_terms()

Attaches a post to a term (taxonomy element). For example, places a post in the specified category.

wp_set_post_categories()

Sets categories for a post.

wp_set_post_tags()

Sets tags for a post.

wp_set_post_terms()

Sets the terms for specified post (sets categories for post).