Getting posts by taxonomy

I usually use the tax_query parameter:

$args = array(
    'post_type'      => 'my_cpt_name',
    'post_status'    => 'publish',
    'posts_per_page' => -1,
    'tax_query'      => array( array(
            'taxonomy' => 'uom_system',
            'field'    => 'slug',
            'terms'    => 'metric-system'
            ) )
    );

$results = get_posts( $args );

See http://codex.wordpress.org/Class_Reference/WP_Query#Taxonomy_Parameters