Question

I want to exclude one of the skill-types that are called in the code below, is this possible?

<ul>
    <li><a href="#" class="all active"><?php _e('All', 'framework'); ?></a><span>/</span></li>
    <?php 
        wp_list_categories(array(
            'title_li' => '', 
            'taxonomy' => 'skill-type', 
            'walker' => new Portfolio_Walker(),
            'show_option_none' => ''
        ));
    ?>
</ul>

Answer 1

Have you checked the Documentation?

You can use the exclude parameter to define a comma-separated list of term IDs:

<?php 
    wp_list_categories(array(
        'title_li' => '', 
        'taxonomy' => 'skill-type',
        'exclude' => '1,2,3,4', //Whatever IDs of the terms you want to exclude
        'walker' => new Portfolio_Walker(),
        'show_option_none' => ''
    ));
?>