This indicates a PHP-based web page. index.php is traditionally the default entry point for many PHP applications (blogs, e-commerce stores, CMS platforms). Its presence suggests the website is dynamic, pulling content from a database rather than serving static HTML files.
In the early days of the web (and still in many legacy systems today), developers built websites using PHP and MySQL. To display a dynamic page, they needed a way to tell the database what to show. inurl index php id 1 shop install