Ususally rack rate means the absolute most a hotel can charge for a room. You might look at it posted on the inside of the door along with the fire excape route. Usually is is at least twice whateve you paid for the hotel room. Most hotels hardly ever charge this rate. They use it when they can not get guests to leave after their reservation. At least back when I worked in a hotel, in our state, you could not force a person to leave their room after their reservation expired. Even if the hotel was sold out the next night, they were legally allowed to stay however long as they wanted. So the hotel can charge them their highest posted rate. We only used this one in a while and during the '96 olympics, when you charge whatever you wanted.
At Disney, it does seem to mean their regular rates with no discounts applied.Their rack rates are not as unreasonable as most.