PHP stands for PHP Hypertext processor. You can find the manual here:

PHP is known as a Server Side Scripting Language. This means all of the source code stays on a server and is unavailable to people who do not have access to the server. The only thing clients can get access to is the end result of the program.

PHP can be used to develop many systems including user systems and login systems, form validation, database management systems, Content management systems, project management systems, and more! PHP is a great programming language for beginners. In this series, we will be diving into all of the concepts you need to know to start developing with PHP.