PHP, which is an abbreviation for PHP: Hypertext Preprocessor, is amongst the most commonly used open-source server-side scripting languages out there. Any site or web-based app built using PHP will run on a given server as long as a PHP module is enabled, which renders the language really universal and it is not that unusual that there are actually several million web servers that support it and hundreds of millions of PHP-driven sites running on them. PHP is preferred over HTML because of the fact that it allows you to build an interactive site with a ton of different features. A PHP-based social network, for example, will serve different web content to each visitor irrespective of the fact that the URL will stay unchanged. On the other hand, HTML websites are static and the page content itself can be updated only manually. Just like any other software program, PHP has different versions and the one that was used while developing a specific website must be enabled on the server in order for the site to behave properly.
