PHP & mod_php

In Web programming, PHP is a script language and interpreter, similar to JavaScript and Microsoft's VBScript, that is freely available and used primarily on Linux Web servers. PHP (the initials come from the earliest version of the program, which was called Personal Home Page Tools) is a cross-platform alternative to Microsoft's Active Server Page (ASP) technology (which runs only on Microsoft's Windows NT servers). As with ASP, the PHP script is embedded within a Web page along with its HTML. Before the page is sent to a user that has requested it, the Web server calls PHP to interpret and perform the operations called for in the PHP script. An HTML  page that includes a PHP script is given a file name suffix of .php or .php3. Like ASP, PHP can be thought of as dynamic HTML pages, since content will vary based on the results of interpreting the script.

  PHP can be compiled as a module (plug-in) for several webservers (mod_php for Apache, for example).

PHP is free and offered under an open source license. The latest version is PHP3.