PHP is basically a general-purpose scripting language. It is especially suitable for server-side web development. PHP generally runs on a web server. Every PHP code in any requested file can be executed by the PHP runtime. This helps in creation of dynamic web page content. The other utilities of it lay in command-line scripting and client-side GUI applications. PHP is deployable on most of the web servers, numerous operating systems and platforms. It can also be used with many relational database management systems. PHP Group supplies the complete source code for users to develop, modify and expand for their own use. So it is offered free of charge.
PHP mainly operates as a filter. It takes input from a file or stream which contains text and/or PHP instructions and produces output of another stream of data. The most common output is HTML. Since the advent of PHP 4, the PHP parser compiles input to give bytecode output for processing by the Zend Engine. It results in an enhanced performance over its interpreter predecessor.
It was originally developed to create dynamic web pages. It now focuses mainly on server-side scripting. It acts quite similar to other server-side scripting languages that provide dynamic content from a web server to a client. Some of its market competitors are Microsoft’s Active Server Pages, Sun Microsystems’ JavaServer Pages, and mod perl.
It has also focused on the development of many frameworks that give building blocks and a design structure to support rapid application development (RAD). Some of these are, viz, CakePHP, Symfony, CodeIgniter, and Zend Framework. All of them offer features similar to other web application frameworks.
PHP is the P in the bundle called LAMP architecture in web industry alongside Linux, Apache and MySQL. The bunch is a way of deploying web applications. P may also refer to Perl or Python or some combination of the three.