mg/dl is the (system/method) that the US uses to express how much blood sugar is contained in a given volume of blood

So if you use a SMBG "stick test meter" to measure your blood and the number was say 150 that would mean

That in your case, the meter extrapolates that there is 150 milligrams of sugar in 1 deciliter of blood

Or in plain english - if you drained about 3.4oz of your blood into a beaker and then sucked out the sugar content, there would be 0.005 ounces of sugar in the suspension

It's just a whole lot easier to say "my blood sugar reading or BG is 150" 😁

And in the case of an insulin user who "dynamically doses" their insulin, eventually you would know that if my BG is 150 and I was expecting it to be "below 140" that would mean I need to add a couple extra units of insulin to my injection (pure made up example)

If you "static dose" where the Doc tells you "inject X units at night or before a meal" and you test and the mg/dl is "out of whack" from what is expected, then you would see your Doc again and (they) would adjust the dosage of your insulin