What's the difference between MariaDB and MySQL? I'm not very familiar with both. I'm primarily a front end developer for the most part.

Are they syntactically similar? Where do these two query languages differ?

Wikipedia only mentions the difference between licensing:


  MariaDB is a community-developed branch of the MySQL database, the
  impetus being the community maintenance of its free status under GPL,
  as opposed to any uncertainty of MySQL license status under its
  current ownership by Oracle.


MariaDB is a backward compatible, binary drop-in replacement of MySQL. What this means is:


Data and table definition files (.frm) files are binary compatible.
All client APIs, protocols and structs are identical.
All filenames, binaries, paths, ports, sockets, and etc... should be the same.
All MySQL connectors work unchanged with MariaDB.
The mysql-client package also works with MariaDB server.


In most common practical scenarios, MariaDB version 5.x.y will work exactly like MySQL 5.x.y, MariaDB follows the version of MySQL, i.e. it's version number is used to indicate with which MySQL version it's compatible.
MariaDB originated as a fork of MySQL by Michael "Monty" Widenius, one of the original developers of MySQL and co-founder of MySQL Ab. The MariaDB Foundation acts as the custodian of MariaDB.
The main motivation behind MariaDB was to provide a floss version of MySQL, in case Oracle goes all corporate with MySQL. It's worth noting that Monty was vocal against MySQL acquisition (via Sun's acquisition) by Oracle.
Although MariaDB is supposed to be compatible with MySQL, for one reason or the other there are quite a few compatibility issues and different features:

MariaDB includes all popular open source engines,

MariaDB claims several speed improvements over MySQL, and

there are a few new floss extensions that MySQL lacks
Finally, the name comes from Monty's daughter Maria (the other one being My), as MySQL is now a registered trademark of Oracle Corporation.


