Reply To: WordPress: show title of the term (custom taxonomy) inside the custom post type

[Senff]

What if a product is attached to more than one category?

Either way, try this perhaps:

$custom_taxonomy = get_the_terms(0, 'category');
if ($custom_taxonomy) {
    foreach ($custom_taxonomy as $custom_tax) {
        echo $custom_tax->slug;
    }
}

Replace ‘category’ (in the first line) with the actual name of your custom taxonomy.