What’s the difference between non alcoholic wine and grape juice?

Non alcoholic wine comes from grape juice. The grape juice has been fermented and yeast has converted the sugar into alcohol and carbon dioxide. This resulting wine (usually) has no sugar left. At this point the wine has the alcohol removed (by sublimation, vacuumed off) and the resulting is non alcoholic wine. It may have no sugar (sweetness), but usually some sugar is added back in to make it more “drinkable.”