How to use the vBulletin relative path option?
The relative path option allows you to move your vBulletin index file outside of the main script folder and put it in the root folder for your web site. For example, if you have a vBulletin installation in the public_html/forum/ folder and there isn’t another index file in the public_html/ directory, you can move the vBulletin one there.
The VB_RELATIVE_PATH constant was introduced in the vBulletin 4 version. It can be set by editing the vBulletin index.php file.
Uncomment the following line and set the relative path to the vBulletin folder:
define(‘VB_RELATIVE_PATH’, ‘forum‘);
If the script is installed in a folder with a different name, replace forum with it.
In this way, once the visitors open your web site through your domain they will be automatically redirected to the vBulletin forum folder.