PHP 4.x

PHP (a recursive acronym for "PHP: Hypertext Preprocessor") is a very popular and widely used open source scripting environment that is used for Web development. It is similar to ASP, but, some would argue, is much easier to learn and implement without lacking any power for more professional users/programmers. PHP is embedded into standard HTML and runs server-side, so, unlike client-side scripting like JavaScript, end users will not be able to see your PHP code.

If you are interested in learning more about PHP, see the PHP manual at PHP.net.