Lactose, most of us know what it is and some of us like myself don't tolerate it very well but OMG you can make some amazing beer styles with this stuff. If you are looking to make a flavored beer you should consider this as the sweetness is smooth and non-fermentable. Plus AIH ships it in a nice durable bag so it arrives safe too.
Adds body and mouth feel. Thickens up your brew....great for stouts. I once added this to an IPA by mistake....that turned out great too!