PHP is a general-purpose scripting language well-suited for server-side web development that runs on web servers. It allows creation of dynamic web page content by executing PHP code within requested files. PHP is portable across most web servers, operating systems, and platforms and can interface with several database systems. The PHP source code is freely available for users to develop, modify, and expand applications. PHP primarily operates as an interpreter that takes input containing text and PHP instructions and outputs another stream of data commonly in HTML format.