[Adrian Schneider]

It's the table prefix you used on all your vbulletin tables... you specify it when installing.

If you installed using "vb3_" then

PHP Code:

$db->query_read("
    SELECT *
    FROM " . TABLE_PREFIX . "user
    WHERE userid = '" . $vbulletin->userinfo['userid'] . "'
    LIMIT 1
"); 


would query the correct table, whereas

PHP Code:

$db->query_read("
    SELECT *
    FROM user
    WHERE userid = '" . $vbulletin->userinfo['userid'] . "'
    LIMIT 1
"); 


would not, because the table is called "vb3_user", not "user".

If you don't have table prefixes, it won't affect anything (because the constant is equal to "").