Table name prefix.
If you only have access to a single database and wish to install more than one version of MediaWiki, or have other applications that also use the database, you can give the table names a unique prefix to stop any naming conflicts or confusion.
For example, if you use the prefix 'wiki_' then the table 'page' will be named 'wiki_page' instead.
You need to set this at the time of initial configuration, or manually change the table names at a later date.
Changing this setting does not automatically update the names of the tables in your database.
This setting is not used if your database is Postgres: instead, schemas are used (see $wgDBmwschema).
Many installers set the database table prefix "$wgDBprefix" to "mw_" by default.
Do not change $wgDBprefix after Setup.php has been included. Note:Setup.php initializes various paths, includes some common files, starts sessions, and performs various other setup tasks for a request. It is not related to the installation or setup of MediaWiki.
If you configure $wgDBservers or $wgLBFactoryConf, you still need to define $wgDBprefix. The combination of $wgDBname, $wgDBmwschema, and $wgDBprefix define the current wiki's database domain. This is also called the local database domain. The 'dbname' and 'tablePrefix' settings in $wgDBservers and $wgLBFactoryConf only define the default DB/prefix when a connection is requested with DatabaseDomain::newUnspecified()->getId() (the empty string) as the database domain, e.g. wfGetDB( DB_REPLICA, , '' ). Note that functions calls like wfGetDB( DB_REPLICA ), which simply omit the database domain, are assumed to refer to the local database domain.