PHP or "PHP: Hypertext Preprocessor" is an Open Source general-purpose scripting language that is well-suited for Web designing and development and can also be integrated with HTML.  The main purpose of this language is to allow web developers to write dynamically generated web pages quickly.

MySQL is an RDBMS which is used in order to store, retrieve and manage data related to required applications. Apache is an Open Source web server and it is also incorporated within XAMPP. A web-server is required to host a web-application (webpage) on a remote server and is catering to the need of processing the client requests.