The Zend Engine is the core component of the PHP programming language, responsible for interpreting and executing PHP scripts. It converts the high-level code written by developers into machine code that can be executed by the server. This process allows web applications to run efficiently and effectively. Developed by Zend Technologies, the Zend Engine has undergone several updates since its initial release, improving performance and adding new features. It plays a crucial role in the overall functionality of PHP, making it a popular choice for web development and server-side scripting.