PHP, known as Hypertext Preprocessor, is the most widely used open-source and general-purpose server-side scripting language utilised mainly in web development to build static or dynamic websites and web applications.
An example of how PHP works:
When someone visits your WordPress site, before sending any files to that visitor, your server first runs the PHP code contained in the WordPress core and any themes or plugins you have installed on your site.
Once your server has processed the code, it delivers the output of all that PHP (the HTML code that a visitor’s browser receives).
In the end, unlike HTML, your website’s visitors will never see the PHP code that powers your WordPress site. Instead, they will see the already processed code your server delivers to their browser.