PHP runs on the server. When a browser asks for catalog.php, the server runs the code in it and sends what that code printed: usually HTML, sometimes JSON, CSV or an image. Linux runs the processes, Apache 129 accepts the connection and hands .php paths to PHP, MySQL 524 stores the data, and PHP turns a request plus some rows into a response. Forms, sessions, logins, PDO queries (Databases with PDO) and API calls all live in PHP; Laravel 2,157 (Laravel) organizes those jobs rather than replacing them.
PHP remains the web's dominant server-side language. W3Techs 13,241 ' survey of 23 September 2026 finds it on 69.9% of the websites whose server-side language it can detect. Of those PHP sites, 64.2% run PHP 8, 28.0% PHP 7 and 7.8% PHP 5, so more than a third run a major version that no longer receives security fixes. WordPress 48 , Drupal 2,652 and MediaWiki 3,259 are all PHP applications.
The architecture has a name: shared nothing. Every request starts with an empty set of variables, runs to completion and throws its state away. Anything that must persist goes into MySQL, a session, a cache or a file. Any worker on any server can take any request, and a fatal error cannot poison the next.