wp_delete_term( int $term, string $taxonomy, array|string $args = array() )

function wp_delete_term( $term, $taxonomy, $args = array() ) {
	global $wpdb;

	$term = (int) $term;

	if ( ! $ids = term_exists($term, $taxonomy) )
		return false;
	if ( is_wp_error( $ids ) )
		return $ids;

	$tt_id = $ids['term_taxonomy_id'];

	$defaults = array();

	if ( 'category' == $taxonomy ) {
		$defaults['default'] = get_option( 'default_category' );
		if ( $defaults['default'] == $term )
			return 0; // Don't delete the default category
	}

	$args = wp_parse_args($args, $defaults);

	if ( isset( $args['default'] ) ) {
		$default = (int) $args['default'];
		if ( ! term_exists( $default, $taxonomy ) ) {
			unset( $default );
		}
	}

	if ( isset( $args['force_default'] ) ) {
		$force_default = $args['force_default'];
	}

	/**
	 * Fires when deleting a term, before any modifications are made to posts or terms.
	 *
	 * @since WP-4.1.0
	 *
	 * @param int    $term     Term ID.
	 * @param string $taxonomy Taxonomy Name.
	 */
	do_action( 'pre_delete_term', $term, $taxonomy );

	// Update children to point to new parent
	if ( is_taxonomy_hierarchical($taxonomy) ) {
		$term_obj = get_term($term, $taxonomy);
		if ( is_wp_error( $term_obj ) )
			return $term_obj;
		$parent = $term_obj->parent;

		$edit_ids = $wpdb->get_results( "SELECT term_id, term_taxonomy_id FROM $wpdb->term_taxonomy WHERE `parent` = " . (int)$term_obj->term_id );
		$edit_tt_ids = wp_list_pluck( $edit_ids, 'term_taxonomy_id' );

		/**
		 * Fires immediately before a term to delete's children are reassigned a parent.
		 *
		 * @since WP-2.9.0
		 *
		 * @param array $edit_tt_ids An array of term taxonomy IDs for the given term.
		 */
		do_action( 'edit_term_taxonomies', $edit_tt_ids );

		$wpdb->update( $wpdb->term_taxonomy, compact( 'parent' ), array( 'parent' => $term_obj->term_id) + compact( 'taxonomy' ) );

		// Clean the cache for all child terms.
		$edit_term_ids = wp_list_pluck( $edit_ids, 'term_id' );
		clean_term_cache( $edit_term_ids, $taxonomy );

		/**
		 * Fires immediately after a term to delete's children are reassigned a parent.
		 *
		 * @since WP-2.9.0
		 *
		 * @param array $edit_tt_ids An array of term taxonomy IDs for the given term.
		 */
		do_action( 'edited_term_taxonomies', $edit_tt_ids );
	}

	// Get the term before deleting it or its term relationships so we can pass to actions below.
	$deleted_term = get_term( $term, $taxonomy );

	$object_ids = (array) $wpdb->get_col( $wpdb->prepare( "SELECT object_id FROM $wpdb->term_relationships WHERE term_taxonomy_id = %d", $tt_id ) );

	foreach ( $object_ids as $object_id ) {
		$terms = wp_get_object_terms( $object_id, $taxonomy, array( 'fields' => 'ids', 'orderby' => 'none' ) );
		if ( 1 == count($terms) && isset($default) ) {
			$terms = array($default);
		} else {
			$terms = array_diff($terms, array($term));
			if (isset($default) && isset($force_default) && $force_default)
				$terms = array_merge($terms, array($default));
		}
		$terms = array_map('intval', $terms);
		wp_set_object_terms( $object_id, $terms, $taxonomy );
	}

	// Clean the relationship caches for all object types using this term.
	$tax_object = get_taxonomy( $taxonomy );
	foreach ( $tax_object->object_type as $object_type )
		clean_object_term_cache( $object_ids, $object_type );

	$term_meta_ids = $wpdb->get_col( $wpdb->prepare( "SELECT meta_id FROM $wpdb->termmeta WHERE term_id = %d ", $term ) );
	foreach ( $term_meta_ids as $mid ) {
		delete_metadata_by_mid( 'term', $mid );
	}

	/**
	 * Fires immediately before a term taxonomy ID is deleted.
	 *
	 * @since WP-2.9.0
	 *
	 * @param int $tt_id Term taxonomy ID.
	 */
	do_action( 'delete_term_taxonomy', $tt_id );
	$wpdb->delete( $wpdb->term_taxonomy, array( 'term_taxonomy_id' => $tt_id ) );

	/**
	 * Fires immediately after a term taxonomy ID is deleted.
	 *
	 * @since WP-2.9.0
	 *
	 * @param int $tt_id Term taxonomy ID.
	 */
	do_action( 'deleted_term_taxonomy', $tt_id );

	// Delete the term if no taxonomies use it.
	if ( !$wpdb->get_var( $wpdb->prepare( "SELECT COUNT(*) FROM $wpdb->term_taxonomy WHERE term_id = %d", $term) ) )
		$wpdb->delete( $wpdb->terms, array( 'term_id' => $term ) );

	clean_term_cache($term, $taxonomy);

	/**
	 * Fires after a term is deleted from the database and the cache is cleaned.
	 *
	 * @since WP-2.5.0
	 * @since WP-4.5.0 Introduced the `$object_ids` argument.
	 *
	 * @param int     $term         Term ID.
	 * @param int     $tt_id        Term taxonomy ID.
	 * @param string  $taxonomy     Taxonomy slug.
	 * @param mixed   $deleted_term Copy of the already-deleted term, in the form specified
	 *                              by the parent function. WP_Error otherwise.
	 * @param array   $object_ids   List of term object IDs.
	 */
	do_action( 'delete_term', $term, $tt_id, $taxonomy, $deleted_term, $object_ids );

	/**
	 * Fires after a term in a specific taxonomy is deleted.
	 *
	 * The dynamic portion of the hook name, `$taxonomy`, refers to the specific
	 * taxonomy the term belonged to.
	 *
	 * @since WP-2.3.0
	 * @since WP-4.5.0 Introduced the `$object_ids` argument.
	 *
	 * @param int     $term         Term ID.
	 * @param int     $tt_id        Term taxonomy ID.
	 * @param mixed   $deleted_term Copy of the already-deleted term, in the form specified
	 *                              by the parent function. WP_Error otherwise.
	 * @param array   $object_ids   List of term object IDs.
	 */
	do_action( "delete_{$taxonomy}", $term, $tt_id, $deleted_term, $object_ids );

	return true;
}