Manual:AdminSettings.php

Overview
The file AdminSettings.sample in your main directory (f.i., /localhost/wiki/) should be copied to AdminSettings.php, and modified to reflect local settings.

It is required for the maintenance scripts which run on the command line, as an extra security measure to allow using a separate user account with higher privileges to do maintenance work..

Wikidb Administrator's username and password
The $wgDBadminuser and $wgDBadminpassword variables identify a SQL user who will be enabled to all database maintenance scripts (see directory maintenance/). Default settings are: The SQL user must be manually created or set to an existing user with necessary permissions. This is not to be confused with sysop accounts for the wiki.

Security
Keep in mind that the AdminSettings.php permissions should not allow other users to view this file as it contains security-related data, including your database user password. chmod 700 or otherwise set the permissions to something that provides security from public access. Generally a separate MySql user is specified in AdminSettings.php to the user in LocalSettings.php which has superuser database permissions to run the maintenance scripts.

Enabling/Disabling profileinfo.php
The wgEnableProfileInfo variable enables the profileinfo.php script. The default value is:

Merging with LocalSettings.php
If the separate user is not needed, you can just put the content into LocalSettings.php, e.g., via $wgDBadminuser = $wgDBuser = 'nurdsome'; $wgDBadminpassword = $wgDBpassword = 'tweedowitz'; there, as in Manual:Wiki family, eliminating the need for.