PHP Constants
A PHP cosntant is an identifier which value cannot be changed during the script. A valid constant name start with letter or underscore(no other special character or number). Syntax: define(name, value, case-insensitive) Example: <?php define("GREETING", "Welcome to W3Schools.com!"); echo GREETING; ?> Array constant in PHP: <?php define("cars", [ "Alfa Romeo", "BMW", "Toyota" ]); echo cars[0]; ?> Constants are global in PHP you can use it anywhere see below example: <?php define("GREETING", "Welcome to W3Schools.com!"); function myTest() { echo GREETING; } myTest(); ?>