In Japan, sushi has been popular as a feast dish to serve to a crowd for quite some time. I am not talking about nigiri sushi, however, where a small morsel of vinegar-seasoned rice is topped with a sliver of raw fish or other ingredient.
Although this is known as the sushi around the world, there are many other kinds of sushi — in fact, the word "sushi" refers to any dish that's made with a vinegar-seasoned rice (the sushimeshi or shari) as the base.
Nigiri sushi has to be eaten as soon as it's made since its toppings are raw, but many other types of sushi can keep for several hours. The vinegar, salt and sugar used to flavor the rice base help to keep it moist and fresh for longer than plain steamed rice so, when combined with cooked ingredients, sushi becomes an ideal make-ahead dish.