constant (PHP 4 >= 4.0.4, PHP 5) constant – Returns the value of a constant Description mixed constant ( string name )constant() will return the value of the constant indicated by name. constant() is useful if you need to retrieve the value of a constant, but do not know its name. I.e. it is stored in a variable or returned by a function. This function works also with class constants.
Example: define(‘MYCONSTANT’, ‘HELLO’);
echo constant(‘MYCONSTANT’);
HELLO // result
source:http://www.php.net/constant