PHP files contain code written in the PHP scripting language. PHP is a widely-used open source general-purpose scripting language that is especially suited for web development. It can be embedded into HTML. Instead of having lots of commands to output HTML, PHP pages contain HTML with embedded code that does something (in this case, output something). The PHP code is executed on the server, generating HTML which is then sent to the client. This allows for dynamic web pages that can interact with databases, handle user input, and perform other server-side tasks. PHP files are typically used to create dynamic web pages, web applications, and server-side scripts. They are often used in conjunction with HTML, CSS, and JavaScript to create complete web applications. PHP is a powerful and versatile language that is used by many popular websites and applications.