add a category term if it doesn't exist (wordpress)

gistfile1.php

<?php

if ( ! term_exists( 'free-flow', 'category' ) ) {
    wp_insert_term( 'Free Flow', 'category',
        array(
            'description'=> 'Give extra left-right padding to the text block',
            'slug' => 'free-flow',
        ) 
    );
}