As I said earlier, I don't know what it is; but due to the fact that in the rate rules it says ID required, I would venture to guess that it is either a company, or a travel group similar to AAA where one would have some kind of ID or membership card. Whether the front desk asks for it or not is what is being bantered about here and while it seems to be the general consensus that they don't, keep in mind murphy's law and buyer beware. If you use this code and they ask for ID, then be prepared to deal with it.