What is MySQL?
MySQL is a multithreaded, multi-user, SQL Database Management System (DBMS).
A database management system (DBMS) is a computer program (or more typically, a suite of them) designed to manage a database (a large set of structured data), and run operations on the data requested by numerous clients.
MySQL is popular for web applications such as MediaWiki or PHP-Nuke and acts as the database component of the LAMP and WAMP platforms (Linux/Windows-Apache-MySQL-PHP/Perl/Python). Its popularity as a web application is closely tied to the popularity of PHP.