PHP is a reflective programming language originally designed for producing dynamic web pages. PHP is used mainly in server-side scripting, but can be used from a command line interface or in standalone graphical applications. Textual User Interfaces can also be created using ncurses. PHP is a recursive acronym for "PHP: Hypertext Preprocessor".

The main implementation is produced by The PHP Group and released under the PHP License. It is considered to be free software by the Free Software Foundation. This implementation serves to define a de facto standard for PHP, as there is no formal specification.

Currently, two major versions of PHP are being actively developed: 5.x and 4.4.x; on July 13, 2007, the PHP group announced that active development on PHP4 will cease by December 31, 2007, however, critical security updates will be provided until August 8, 2008.