Balsamic vinegar
It is one of the most ancient products, and unfortunately, one of the most ill-treated too.
Up to now it is not possible to enter a shop and ask, generically, for “ A balsamic vinegar, please!”. The risk you would run is very high: they might palm off on you something that doesn't respect the tradition at all! ( At first I wrote that you would be given “ a slop” but I realized it would have been politically unfair.)
When you ask for a Balsamic Vinegar, you must have clear ideas, and we are here to help you out!