PHP, which is a recursive acronym for PHP: Hypertext Preprocessor, is one of the most commonly used web programming languages that are available out there. Any site or Internet app created with PHP will run on a given web server as long as a PHP module is activated, which renders the language absolutely universal and it is not a big surprise that there are a couple of million servers that support it and hundreds of millions of PHP-driven websites running on them. PHP is preferred over HTML because of the fact that it allows you to set up an interactive site with heaps of different features. A PHP-based community website, for example, will display different content to each visitor regardless of the fact that the page URL will be the same. On the other hand, HTML websites are static and the content on the pages can be modified only manually. Like any other software, PHP has different versions and the version that was used whilst setting up a specific website must be available on the server in order for the site to work flawlessly.