MySQL is the most popular open-source database. As an open-source project, it can be forked and distributed under a new name. MariaDB is not just a fork of MySQL, but an open-source project led my Monty Widenius, the original author of MySQL. MariaDB thus promises a large degree of MySQL compatibility, while also improving on it in many important ways.
In this talk from 2012, Max Mether introduces MariaDB, comparing it with MySQL and indicating how its many improvements make it a strong candidate to replace MySQL, now and in the future.