Hvad er database host?

Jeg kan ikke finde ud af hvad min database host er.
Her er mit script:
<?php

define('DB_NAME', '');
define('DB_USER', '');
define('DB_PASSWORD', '');
define('DB_HOST', '');

$link = mysql_connect(DB_HOST, DB_USER, DB_PASSWORD);

if (!$link){
    die('Could not connect: ' . mysql_error());
}

$db_selected = mysql_select_db(DB_NAME, $link);

if (!$db_selected){
    die('Can\'t use ' .DB_NAME . ': ' . mysql_error());
}


echo 'Connected successfully';

?>