Case-sensitive constant name

                
                    <?php
                    // case-sensitive constant name
                    define("GREETING", "Welcome to W3Schools.com!");
                    echo GREETING;
                    ?>
                
                

Case-insensitive constant name

                
                    <?php
                    // case-insensitive constant name
                    define("GREETING", "Welcome to W3Schools.com!", true);
                    echo greeting;
                    ?>
                
                

Create a Array constant with define()

                
                    <?php
                    define("cars", [
                      "Alfa Romeo",
                      "BMW",
                      "Toyota"
                    ]);
                    echo cars[0];
                    ?> 
                
                

Use a constant inside a function (when it is defined outside the function)

                
                    <?php
                    define("GREETING", "Welcome to W3Schools.com!");
                    
                    function myTest() {
                      echo GREETING;
                    }
                     
                    myTest();
                    ?>