PHP, which stands for "PHP: Hypertext Preprocessor", is an open-source HTML-embedded scripting language. Much of its syntax is borrowed from C, Java and Perl with some unique features thrown in. The main goal of the language is to allow web developers to write dynamically generated pages 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.