If it's diabetes, type 2 is where your body doesn't produce enough insulin. Usually because it's not absorbing or diminished production capacity.
Type 3 is where sugars don't pass the blood brain barrier thus starving your brain of nutrients. The symptoms look like alzheimer's, so it's usually diagnosed post mortem.
Type 2 is adult onset diabetes. Type 3 is the term used by those referring to diabetes, and alzheimer's disease connection. AGEs (Accelerated Glycation End products) form when serum glucose levels are too high, too much of the time and the sugars "glycate" i.e. bind onto, proteins making them non-functional.