What is Perl?
Perl is an interpreted high-level programming language developed by Larry Wall. Perl has become the premier scripting language of the Web, as most CGI programs are written in Perl. However, Perl is widely used as a rapid prototyping language and a "glue" language that makes it possible for different systems to work well together. Perl is popular with system administrators who use it for an infinite number of automation tasks. Perl's roots are in UNIX but you will find Perl on a wide range of computing platforms. Because Perl is an interpreted language, Perl programs are highly portable across systems.
http://www.perl.com

What is PHP?
PHP is a server-side scripting language for creating dynamic Web pages. PHP's programming syntax is very similar to that of Perl. Because of its elegant design, PHP makes it easy for anyone to learn. It is significantly easier than comparable Perl or ASP Code. Unlike other scripting languages, PHP supports the most common databases like Oracle, Sybase and MySQL. It is also possible to integrate external libraries to generate PDF documents or parsing XML PHP is an open-source language and is supported by a large groups of delvelopers. The code is downloadable from php.net.
http://www.php.net

What is MySQL?
MySQL is a relational database management system. It is a Open Source SQL database provided by MySQL AB. MySQL is very fast, reliable, and easy to use. It also has a very practical set of features developed in very close cooperation with our users. MySQL was originally developed to handle very large databases much faster than existing solutions and has been successfully used in highly demanding production environments for several years. Though under constant development, MySQL today offers a rich and very useful set of functions. The connectivity, speed, and security make MySQL highly suited for accessing databases on the Internet.
http://www.mysql.com