PHP (PHP: Hypertext Preprocessor) is a general-purpose programming language widely used for server-side web applications. Joomla’s core and many extensions are written in PHP: the server executes their code and sends the resulting response to the browser.
How PHP generates a page
The web server passes a request to a PHP handler. The application checks input and permissions, reads data and produces HTML or another response. The browser normally receives the output rather than PHP source code. HTML and CSS provide structure and presentation, while JavaScript can control interface behaviour.
PHP-FPM, CLI and PHP extensions
PHP-FPM manages PHP processes serving web requests. CLI runs PHP from the command line, for example for background jobs. A website and CLI can use different PHP versions, php.ini settings and modules. A version reported in a terminal therefore does not necessarily identify the PHP handler serving Joomla.
PHP extensions add capabilities to the runtime, such as database access, image processing and international string handling. They are distinct from Joomla components, modules and plugins.
Versions and compatibility
Choose a supported PHP branch compatible with the installed Joomla release, template and every extension. A minimum requirement indicates a baseline, not necessarily the best choice for a new project. Check PHP’s current schedule for active and security support.
Before switching versions, make a backup and test a copy of the website in a separate environment. Afterwards, check the actual web handler, login, forms, background jobs and error logs. An older extension may be incompatible even when Joomla’s core supports the chosen PHP branch.
Summary
PHP executes Joomla’s server-side logic. Reliable operation depends on whole-site compatibility, the required PHP modules and checking the environment that actually handles web requests.