If food is scrumptious, it tastes very, very good — rich, moreish, the kind of cake or meal you praise out loud. It is informal and a little playful, stronger and fussier than nice, close to delicious but warmer, the word on a biscuit tin or in a home kitchen. British speakers use it a lot about puddings, chocolate, and Sunday lunch; American speakers use it too, though it can sound a bit old-fashioned or cute. People almost always say it about food; you might hear it stretched to a room or a dress as a joke, but that is extra. It is not a restaurant-critic word in the stiff sense — too friendly for that. Where the word comes from, scholars do not agree, so I will not pretend there is one tidy story.