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<p>PHP is a general-purpose scripting language that is especially suited for <a href="http://en.wikipedia.org/wiki/Web_development" title="Web development">web development</a>. It is the fourth most popular computer programming language, ranking behind <a href="http://en.wikipedia.org/wiki/Java_%28programming_language%29" title="Java (programming language)">Java</a>, <a href="http://en.wikipedia.org/wiki/C_%28programming_language%29" title="C (programming language)">C</a>, and <a href="http://en.wikipedia.org/wiki/Visual_Basic" title="Visual Basic">Visual Basic</a>. PHP generally runs on a <a href="http://en.wikipedia.org/wiki/Web_server" title="Web server">web server</a>, taking PHP code as its input and creating <a href="http://en.wikipedia.org/wiki/Web_page" title="Web page">web pages</a> as output. It can also be used for <a href="http://en.wikipedia.org/wiki/Command-line" class="mw-redirect" title="Command-line">command-line</a> scripting and <a href="http://en.wikipedia.org/wiki/Client-side" title="Client-side">client-side</a> <a href="http://en.wikipedia.org/wiki/Graphical_user_interface" title="Graphical user interface">GUI</a> applications. PHP can be deployed on most <a href="http://en.wikipedia.org/wiki/Web_server" title="Web server">web servers</a>, many <a href="http://en.wikipedia.org/wiki/Operating_system" title="Operating system">operating systems</a> and <a href="http://en.wikipedia.org/wiki/Platform_%28computing%29" class="mw-redirect" title="Platform (computing)">platforms</a>, and can be used with many <a href="http://en.wikipedia.org/wiki/Relational_database_management_system" title="Relational database management system">relational database management systems</a>. It is available free of charge, and the PHP Group provides the complete source code for users to build, customize and extend for their own use.</p>
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<p>PHP primarily acts as a <a href="http://en.wikipedia.org/wiki/Filter_%28software%29" title="Filter (software)">filter</a>, taking input from a file or stream containing text and/or PHP instructions and outputs another stream of data; most commonly the output will be HTML. From PHP 4, the PHP <a href="http://en.wikipedia.org/wiki/Parser" class="mw-redirect" title="Parser">parser</a> <a href="http://en.wikipedia.org/wiki/Compiler" title="Compiler">compiles</a> input to produce <a href="http://en.wikipedia.org/wiki/Bytecode" title="Bytecode">bytecode</a> for processing by the <a href="http://en.wikipedia.org/wiki/Zend_Engine" title="Zend Engine">Zend Engine</a>, giving improved performance over its <a href="http://en.wikipedia.org/wiki/Interpreter_%28computing%29" title="Interpreter (computing)">interpreter</a> predecessor.</p>
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<p>Originally designed to create dynamic web pages, PHP's principal focus is <a href="http://en.wikipedia.org/wiki/Server-side_scripting" title="Server-side scripting">server-side scripting</a>, and it is similar to other server-side scripting languages that provide dynamic content from a web server to a <a href="http://en.wikipedia.org/wiki/Client_%28computing%29" title="Client (computing)">client</a>, such as <a href="http://en.wikipedia.org/wiki/Microsoft" title="Microsoft">Microsoft</a>'s <a href="http://en.wikipedia.org/wiki/ASP.NET" title="ASP.NET">ASP.NET</a> system, <a href="http://en.wikipedia.org/wiki/Sun_Microsystems" title="Sun Microsystems">Sun Microsystems</a>' <a href="http://en.wikipedia.org/wiki/JavaServer_Pages" title="JavaServer Pages">JavaServer Pages</a>, and <a href="http://en.wikipedia.org/wiki/Mod_perl" title="Mod perl">mod_perl</a>. PHP has also attracted the development of many <a href="http://en.wikipedia.org/wiki/Software_framework" title="Software framework">frameworks</a> that provide building blocks and a design structure to promote <a href="http://en.wikipedia.org/wiki/Rapid_application_development" title="Rapid application development">rapid application development</a> (RAD). Some of these include <a href="http://en.wikipedia.org/wiki/CakePHP" title="CakePHP">CakePHP</a>, <a href="http://en.wikipedia.org/wiki/PRADO" title="PRADO">PRADO</a>, <a href="http://en.wikipedia.org/wiki/Symfony" title="Symfony">Symfony</a> and <a href="http://en.wikipedia.org/wiki/Zend_Framework" title="Zend Framework">Zend Framework</a>, offering features similar to other <a href="http://en.wikipedia.org/wiki/List_of_web_application_frameworks" title="List of web application frameworks">web application frameworks</a>.</p>
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<p>The <a href="http://en.wikipedia.org/wiki/LAMP_%28software_bundle%29" title="LAMP (software bundle)">LAMP</a> architecture has become popular in the web industry as a way of deploying web applications. PHP is commonly used as the <i>P</i> in this bundle alongside <a href="http://en.wikipedia.org/wiki/Linux" title="Linux">Linux</a>, <a href="http://en.wikipedia.org/wiki/Apache_HTTP_Server" title="Apache HTTP Server">Apache</a> and <a href="http://en.wikipedia.org/wiki/MySQL" title="MySQL">MySQL</a>, although the <i>P</i> can also refer to <a href="http://en.wikipedia.org/wiki/Python_%28programming_language%29" title="Python (programming language)">Python</a> or <a href="http://en.wikipedia.org/wiki/Perl" title="Perl">Perl</a>.</p>
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<p>As of April 2007, over 20 million Internet domains were hosted on servers with PHP installed, and PHP was recorded as the most popular Apache module.</p>
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<p class="attribution">This excerpt is adapted from <a href="http://en.wikipedia.org/wiki/PHP#Use">Wikipedia: PHP - use</a>. It is used here under a <a href="http://en.wikipedia.org/wiki/Wikipedia:Text_of_Creative_Commons_Attribution-ShareAlike_3.0_Unported_License">Creative Commons BY-SA 3.0</a> license.</p>
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