Definition: Server side scripting means that all of the code is executed on the server before the data is passed to the user's browser. In the case of PHP this means that no PHP code ever reaches the user, it is instead executed and only the information it outputs is sent to the web browser.
One way to see this in action is to open one of your PHP pages in a web browser and then choose the 'View Source' option. You will not see any PHP code; you will only see what the PHP has outputted because all of the code was executed on the server before it was delivered to the browser.
Examples:
<?php
$Cat = "Spot";
$Dog = "Clif";
Print "My cat " . $Cat . " and my dog " . $Dog . " like to play together.";
?>
While the PHP file may contain all of the information above, your browser will only ever receive the information: My cat Spot and my dog Clif like to play together.
