MySQL is an open source, relational database management system (RDBMS) often used in conjunction with scripting languages such as Perl and PHP.

An open source application is one where anyone can use and modify the source code, allowing a great deal of flexibility in terms of creating applications. 

MySQL is now arguably the most popular database system on the Internet and is certainly the most popular open source application of its type. Some of the world's best known online brands use MySQL, including Facebook and Google.

Originally developed by Michael Widenius and David Axmark in 1994,  MySQL is now developed, distributed, and supported by Oracle Corporation. 

It was originally created to handle large databases but is also used by many small applications. It is the database technology of choice for high-traffic web sites because of its high performance, stability and ease of use. 

MySQL can be administered via command-line tools for tasks such as querying the database, backing up data and performing common tasks. A GUI (Graphical User Interface) is also available from third party developers; with the most popular being phpMyAdmin - a free application.

Chances are that if a software application you are interested in using on your site requires database support, MySQL will be compatible.