PHP: Hypertext Preprocessor is an open source server side programming language extensively used for web scripts and to process data passed via the Common Gateway Interface from HTML forms etc. PHP can be written as scripts that reside on the server and may produce HTML output that downloads to the web browser. Alternatively, PHP can be embedded within HTML pages that are then saved with a .php file extension. ...
PHP is the widely-used, free, and efficient alternative to competitors such as Microsoft's ASP. PHP is perfectly suited for Web development and can be embedded directly into the HTML code.
The PHP syntax is very similar to Perl and C. PHP is often used together with Apache (web server) on various operating systems. It also supports ISAPI and can be used with Microsoft's IIS on Windows.