SQL is the most popular database language in the world. MySQL is a client/server implementation that consists of a server daemon (mysqld) and many different client programs and libraries. It famously hosts some of the biggest databases in the world and is renowned for high performance. It is commonly used as a back-end for dynamic websites and constitute the M the LAMP stack (Linux Apache MySQL PHP).
The main goals of MySQL are speed, robustness, and ease of use. MySQL was originally developed because the developers at TcX needed an SQL server that could handle very large databases an order of magnitude faster than what any database vendor could offer them.
The official way to pronounce MySQL is "My Ess Que Ell" (Not MY-SEQUEL).