It is how much insulin you make in response to the glucose you have to have in circulation to keep your glucose dependent tissue fueled. Extracting out all the extra insulin you make in response to stimulation by food.
Fasted Insulin is the closest we can get to it.
I make 13.7 mIU/l but a year ago I was making 29 mIU/L so I'm am slowly improving that with time. The longer I am at lower levels of insulin, the more sensitized I become to it, and the less I need to make.