They are referring to the (some think useless) double decker cargo tray that some of us have... Some manufacturers make two diff models of mats (one for vehicles w/o the tray -- and others that will fit either only on top of the tray, or only beneath it, due to the difference in available space w/ the tray installed, or when the tray is in the down position)
This mat on ebay seems to work nicely for vehicles WITH the cargo tray... it can be placed UNDER the tray when the tray is in use, or on TOP of the tray when it is in the down position. Tempted to sell my tan husky liner (made for a vehicle w/o the tray) and get one of these: