It is shorthand code, it basically does this:
if ($page == 'login' || $page == 'register')
{
if (DH_LOGGED)
{
header('Location: '.$config['path'].'?p=me');
exit;
}
}
else
{
if (!DH_LOGGED)
{
header('Location: '.$config['path'].'?p=login');
exit;
}
}
in the one line or similar

