Constants are similar to variables except that they cannot be changed or undefined after they've been defined. Begin the name of your constant with a letter or an underscore. To create a constant, use the define() function:

define(name, value, case-insensitive)

Parameters: name: Specifies the name of the constant; value: Specifies the value of the constant; case-insensitive: Specifies whether the constant name should be case-insensitive. Default is false; The example below creates a constant with a case-sensitive name:

<?php
  define("georgian_player", "Kvicha Kvaratskhelia");
  echo georgian_player;
  // Outputs "Kvicha Kvaratskhelia"
?>

The example below creates a constant with a case-insensitive name:

<?php
  define("georgian_player", "Kvicha Kvaratskhelia", true);
  echo Georgian_Player;
  // Outputs "Kvicha Kvaratskhelia"
?>

No dollar sign ($) is necessary before the constant name.