PHP is a computer programming. WordPress is written entirely in PHP and all of the functionality in a WordPress site comes from PHP.
PHP was created in 1995 and stands for “hypertext preprocessor” although it is always referred to just as PHP. Technically, PHP is a scripting language, meaning that is specifically designed to sit on a web server and then deliver information.
PHP only became standardized in 2014, but its relatively simple structure has made it a powerful tool for websites. The benefit of using PHP versus standard HTML alone is that PHP allows websites to display content dynamically, i.e. automatically updated on the fly rather than having to modify a static HTML page with new content every time you want to make a change.
If you’re new to WordPress and don’t want to do any developing, then you won’t need to understand how PHP works or write anything in the PHP language. You can use, run, and manage your WordPress site without ever having to learn PHP.
For developers, however, anything you can create for a WordPress site, including themes, widgets, and customized commands, are all written in PHP.
When you install WordPress, you’ll see a number of PHP files in your home directory, identified by having the “.php” extension. Keep in mind, however, that PHP commands can also be contained and executed from inside HTML files.
PHP is a relatively simple programming language, so it isn’t particularly hard to learn. If you want full control over your WordPress website, the three different things you will need to learn are PHP, HTML, and CSS as these determine everything about how your website operates, what content is displayed, and how the content looks and is arranged.