Manual:$wgDBserver

Details
Database host name or IP address. Found in.

If you are using MySQL on a non-standard port, you can use the -syntax, for example. Note that using a port number when you specify  as the host name will have no effect, as MySQL will connect through a socket instead. If the MySQL server is on the same server and you want to connect through a socket in a non-standard location, you can use the -location, for example.