It's a plate of material that heats up from microwaving and in turn heats your food too. Without that the microwaves are only exciting the water molecules in your food and steaming your food to heat it. With the special plate, you also get radiant IR heating which causes crisping. (Yum)
I don't know where to find you the product, but that's the best I can recall about it. I hope that helps at least a bit.