Trying to Create a PHP Variable for post_type that can be referenced Site Wide

you can define a constant in wp.config.php or at the beginning of functions.php of your theme

if (!defined('CAROUSEL_CPT')) {
  define("CAROUSEL_CPT", "post");
}

WP_Query('post_type=".CAROUSEL_CPT);//....

Hata!: SQLSTATE[HY000] [1045] Access denied for user 'divattrend_liink'@'localhost' (using password: YES)