PHP, which stands for "PHP: Hypertext Preprocessor" is a widely-used Open Source general-purpose scripting language that is especially suited for Web development and can be embedded into HTML. Its syntax draws upon C, Java, and Perl, and is easy to learn. The main goal of the language is to allow web developers to write dynamically generated webpages quickly, but you can do much more with PHP.
This manual consists primarily of a function reference, but also contains a language reference, explanations of some of PHP's major features, and other supplemental information.
You can download this manual in several formats at http://www.php.net/docs.php. The downloads are updated as the content changes. More information about how this manual is developed can be found in the 'About the manual' appendix.