You can just create a variable to hold define values like this:

$SEMAPHORE_KEY = 12345; 

But this is the PHP correct way to define:

define ('AUTHOR_X_ID',        '16');

if ( $author_id != AUTHOR_X_ID )
{

}

Define an array

define('MY_ARRAY_DEFINE',       array(
    'chair',
    'mat',
    'thing'
));

defined() (ifdef)

  if (defined('MY_DEFINE_NAME'))
    do_something = 1;



  if (!defined('MY_DEFINE_NAME'))
    do_something = 1;


  if (defined('MY_SITE_NAME'))
    $MY_SITE_NAME = MY_SITE_NAME;
  else
    $MY_SITE_NAME = get_site_url();