and

$meta_query = array(
	'relation' => 'AND',
	array(
		'key'     => 'fecha_evento',
		'value'   => 'hoy',
		'compare' => '<',
	),
	array(
		'key'     => 'fecha_termino',
		'value'   => 'hoy',
		'compare' => '>=',
	),
);