Tax q

or

$tax_query = array(
	'relation' => 'OR',
	array(
		'taxonomy'         => 'zzzz',
		'terms'            => 'a',
		'field'            => 'name',
		'operator'         => 'IN',
	),
	array(
		'taxonomy'         => 'wwwww',
		'terms'            => 'b',
		'field'            => 'name',
		'operator'         => 'IN',
	),
);