PHP
PHP is the scripting language in which Moodle is developed. PHP does not stand alone, it is tightly integrated with a suitable HTTP Server. Most people use the Apache HTTP Server for this purpose although a number of others are supported.
PHP describes itself as "a widely-used general-purpose scripting language that is especially suited for Web development and can be embedded into HTML."
Installation
Usually PHP is installed alongside Apache and MySQL in a combination known as AMP, see Installing AMP for details.
Minimum version requirements
The minimum version of PHP required for Moodle is listed in the requirements section of the installation instructions