Show posts from a certain taxonomy

front-page.php

<?php
$loop = new WP_Query(array(
    'post_type'      => 'ad',
    'posts_per_page' => 4,
    'tax_query'      => array(
        // Note: tax_query expects an array of arrays!
        array(
            'taxonomy' => 'type', // my guess
            'field'    => 'slug',
            'terms'    => 'business',
        ),
    ),
));
?>