Constants are PHP containers that remain constant and never change. Constants are used for data that is unchanged at multiple places within a program. Variables are temporary storage while Constants are permanent. Use Constants for values that remain fixed and referenced multiple times.

Rules for defining constant

PHP constants can be defined in 2 ways:

• Using define() function
• Using const keyword

Using define() function

define(name, value, case-insensitive)

name: Name of the constant

value: Value of the constant

case-insensitive: Whether a constant is case-insensitive, The default value is false.

Using const keyword

The const keyword defines constants at compile time. It is a language construct, not a function.

<?php
const MESSAGE = "Welcome to PHP"; 
echo MESSAGE; 
?>