Hello qazw1,

If I am not wrong there is a thread in this forum about it. Used the search function.

Basically they are offering you different room upgrades at special rates, on an standby basis, ie. it is only confirmed at check in.
I am sure other people in this forum will be able to explain it better but to see how it works, try youeself to do a booking at the Hilton web(which you can cancel afterwards), and when you finalize it, very likely you will get the posibility of requesting the mentioned Nor1 upgrades.

Good luck!