PHP is a general-purpose scripting language geared towards web development. It was originally created by Danish-Canadian programmer Rasmus Lerdorf in 1993 and released in 1995. The PHP reference implementation is now produced by the PHP Group. PHP was originally an abbreviation of Personal Home Page, but it now stands for the recursive initialism PHP: Hypertext Preprocessor.

PHP code is usually processed on a web server by a PHP interpreter implemented as a module, a daemon or a Common Gateway Interface (CGI) executable. On a web server, the result of the interpreted and executed PHP code—which may be any type of data, such as generated HTML or binary image data—would form the whole or part of an HTTP response. Various web template systems, web content management systems, and web frameworks exist that can be employed to orchestrate or facilitate the generation of that response. Additionally, PHP can be used for many programming tasks outside the web context, such as standalone graphical applications and robotic drone control. PHP code can also be directly executed from the command line.

The standard PHP interpreter, powered by the Zend Engine, is free software released under the PHP License. PHP has been widely ported and can be deployed on most web servers on a variety of operating systems and platforms.

The PHP language has evolved without a written formal specification or standard, with the original implementation acting as the de facto standard that other implementations aimed to follow.

W3Techs reports that as of December 2023, "PHP is used by 76.6% of all the websites whose server-side programming language we know." It also reports that:

  • 20.1% of PHP users use 8.x versions (most thereof on 8.0 with is no longer supported);
  • 61.3% - most by far use the unsupported PHP 7, more specifically PHP 7.4;
  • 18.3% use PHP 5, which is neither supported with security fixes and is known to have serious security vulnerabilities.

This means the vast majority of PHP websites, e.g. all PHP 7 and PHP 5 websites are vulnerable to hacking; some Linux distributions such as Ubuntu and Debian provide commercial support, and may provide paid-for security patches for e.g. 7.4 of PHP.