What is "Server SQL Mode"?

The MySQL server can operate in different SQL modes, and (as of MySQL 4.1) can apply these modes separately for different clients. Modes define what SQL syntax MySQL should support and what kind of data validation checks it should perform. This makes it easier to use MySQL in different environments and to use MySQL together with other database servers. For more information, see http://dev.mysql.com/doc/mysql/en/server-sql-mode.html