what are sticky posts in wordpress code example

Example: wordpress show only sticky posts

$sticky = get_option( 'sticky_posts' );
$args = array(
        'posts_per_page' => 1,
        'post__in' => $sticky,
        'ignore_sticky_posts' => 1
);
$query = new WP_Query( $args );
if ( isset( $sticky[0] ) ) {
    // insert here your stuff...
}