MySQL is the open-source, relational database that WordPress uses. A database is a collection of structured data that can be accessed with specific commands. The commands that MySQL uses are the Structured Query Language, aka SQL. MySQL is a relational database because the data is stored in tables that have both rows and columns. This makes it easy for the data to have keys that relate (or associate) one piece of data with another.
WordPress stores all your posts, pages, and theme settings in the database, along with a variety of other data. But WordPress is not just a database, it also consists of files such as the WordPress software itself (the PHP code), your images, and the code used by your theme and plugins (also written in PHP).
Most WordPress users only need to know the following four things about their MySQL databases:
1) WordPress recommends MySQL version 5.6, but can run on MySQL 5.0.
2) You should have an automatic backup plan that backs your database up.
3) You need to create a MySQL database and a database user (and password) in order to install WordPress.
4) Your database name, database username, and the username’s password go into your wp-config.php file.