add_action( 'init', 'create_morteza_slider_tax' );

function create_morteza_slider_tax() {
    register_taxonomy(
        'morteza_slider',
        'post',
        array(
            'label' => __( 'Sliders' ),
            'hierarchical' => false,
            'public' => false
        )
    );
}

$query = new WP_Query( [
    'morteza_slider' => 'homepage' // <-- this is all that's needed
] );

// a standard post loop
if ( $query->have_posts() ) {
    echo 'start slider markup';

    while ( $query->have_posts() ) {
        $query->the_post();
        // TODO: output this post as a slide
    }
    wp_reset_postdata();
    echo 'end slider markup';
}