PHP is a server-side scripting language designed especially for the Web. Within an HTML page, you can embed PHP code that will be executed each time the page is visited. Your PHP code is interpreted at the web server and generates HTML or other output that the visitor will see.
PHP is an Open Source project, which means you have access to the source code and use, alter, and redistribute it all without charge.
PHP originally stood for Personal Home Page but was changed in line with the GNU recursive naming convention and now stands for Hypertext Preprocessor. The current major version of PHP is 5. This version saw a complete rewrite of the underlying Zend engine and some major improvement