PHP is everywhere
There are many reasons to understand and enjoy PHP, possibly the most powerful and valid of which is that it is used and executed everywhere. And because it works everywhere and is easy to start, much of the popular software is written in PHP. WordPress is the largest and most familiar instance, but tools like Joomla, Drupal, Magento, MediaWiki and more are running PHP on the server. And there are more PHP application frameworks than you can also shake in Symfony, Zend, Laravel, Aura, CakePHP, Yii and even the renowned CodeIgnitor.