I have learning PHP, but, most of the times, I used to come across the word Zend engine, how it is related to PHP
Zend is a scripting engine that sits below the PHP-specific modules. It was optimized to ensure massively improved performance and extensibility.
With the introduction of the Zend Engine 2, PHP 5 brings new fundamental improvements. The engine provides significantly enhanced support for object-oriented programming. For the first time, objects and object-oriented design lie at the heart of PHP, making it an even more suitable platform for large enterprise applications.