WordPress at a glance
function is not described

wp_create_tag() WP 2.3.0

Add a new tag to the database if it does not already exist.

No Hooks.

Return

Array/WP_Error.

Usage

wp_create_tag( $tag_name );
$tag_name(int/string) (required)

Code of wp create tag: wp-admin/includes/taxonomy.php VER 5.1.1

<?php
function wp_create_tag( $tag_name ) {
	return wp_create_term( $tag_name, 'post_tag' );
}