MySQL is the most widely used relational database management system (RDBMS) for websites. The main reason for it's popularity is that it is an open source. That means it is free for both commercial and personal use. Another reason is that it's available on multiple operating systems like, Linux, AIX, Mac O/s, Solaris and Windows platforms.
MySQL was developed to provide a low-end alternative to powerful proprietary databases.
MySQL comes in two editions, MySQL Community Server and MySQL Enterprise Server. The Community Server is free whereas Enterprise Server is paid.
MySQL is used in many popular website applications like Wordpress, Joomla, Simple Machines Forum, phpBB, MyBB, TYPO3, MODx and Drupal.
MySQL is also used by many internet giants like Facebook, Twitter, YouTube and Flickr.
MySQL was created by a Swedish company, MySQL AB in 1995. It's name is a combination of "My", the name of co-founder Michael Widenius's daughter and "SQL"
In 2008 MySQL is bought by Sun Microsystem, and in 2009 Oracle Corporation bought Sun Microsystem.