PHP is a server-side programming language, which means that it is used on the server side to create dynamic Web pages. It is used to process user input and return a Web page. It can be used to create Web sites, build online forms and validate data and generate dynamic Web pages. PHP enables the websites to store data on server and retrieve the data whenever required. It is the most powerful tool used to develop dynamic web sites. Some of the most popular and widely used applications are WordPress, Facebook, WordPress, Kickstarter and Drupal.