PHP is a server-side scripting language designed for web development but also used as a general-purpose programming language. Originally created by Rasmus Lerdorf in 1994, the PHP reference implementation is now produced by The PHP Group.
It is the most popular language to run websites globally. Most famous Open sources like WordPress, Joomla, Drupal are written in this language. PHP is supported by about all leading and developing web hosting companies.
MySQL is an open-source relational database management system. Its name is a combination of “My”, the name of co-founder Michael Widenius’s daughter, and “SQL”, the abbreviation for Structured Query Language.
As It sounds Database management system, it stores all the data on your website. For example your login details, theme & plugin information, your settings, site name and other important information you have submitted.