In relation to PHP programming language, MySQL is the old database driver, and MySQLi is the Improved driver. MySQLi takes advantage of the newer features of MySQL 5. Lifted verbatim from the php.net site:

Embedded server support Object-oriented interface Support for Prepared Statements Support for Multiple Statements Support for Transactions Enhanced debugging capabilities

You have the choice of using mysql or mysqli.

Reference: http://www.php.net/manual/en/mysqli.overview.php . . . → Read More: What is the difference between mysql and mysqli?