Hello Reader's! In working PHP you might have seen the two common syntax $_SERVER['HTTP_HOST'] and $_SERVER['SERVER_NAME']. They share similar name but they work different.
$_SERVER['SERVER_NAME'] gives the value of the server name as defined in host configuration (lets say example Apache the Apache .conf file) and $_SERVER['HTTP_HOST'] gives you the domain name through which the current request is being fulfilled, here user is more related to request.

HTTP_HOST is the header from the current request, if it exists. Whereas SERVER_NAME is the name of the server host under which the current script is executing. If the script is running on a virtual host then this will be the value defined for that virtual host.

Let's see the working example below:-

<?php
echo $_SERVER['SERVER_NAME'];
?>

Output:

www.findnerd.com

And

<?php echo $_SERVER['HTTP_HOST']; ?>

Output:-

localhost:8080