A user-defined function (UDF) is a way to extend MariaDB with a new function that works like a native (built-in) MariaDB function such as ABS() or CONCAT().
Statements making use of user-defined functions are not safe for replication.
For a collection of existing UDFs see http://www.mysqludf.org/.
CREATE FUNCTION UDFCreate a user-defined function
DROP FUNCTION UDFDrop a user-defined function
mysql.func TableUser-defined function information