PHP stands for Hypertext Preprocessor, an amazing and widely-recognized open source scripting language that is commonly used for websites and can be incorporated into HTML.
Launched more than 25 years ago, it has gained more popularity since it is powerful enough to be at the backbone of WordPress, deep enough to operate complex social networks and simple enough for beginner developers.
Running on the Zend engine (the most common implementation), this scripting language is mainly employed in the building of web servers. It can run both on the browser and in the command line, giving you the option to display your code output either in the browser or in the terminal.