MySQL is an open-source database software system. According to its creators, it is "the world's most popular open source database", and is "used in more than 11 million installations."[1]
It is one of the two databases supported by MediaWiki (the other being PostgreSQL).[2] It is used by Wikipedia®, as well as other wikis that use MediaWiki. MySQL is also reportedly used by Facebook, Twitter and YouTube.
It is a relational database management system (RDBMS) which responds to SQL commands.