B-grade cuisine is popular in Japan, and in the U.S.A., and while there’s no set definition for it–I mean, this isn’t quantum physics–you know it when you taste and see it.
This is fun food–You’re hungry, you’re out with friends, you want to eat and drink in a noisy, convivial place.
In Japan this can include curry chicken, fried octopus, ramen, yakitori, etc. It’s filling, satisfying, and maybe best of all: A night out with drinks won’t cost you more than about $30.
In the U.S., the big difference is that B-grade costs more. Back in the day, a night out with friends in a decent place meant pitchers of draft beers, and wings, dim sum-like appetizers, burgers, sausages, or pizza. This is still true, but nowadays this stuff is all served in places that call themselves restaurants. And charge accordingly. It’s B-grade food with A-grade prices.
Interestingly, restaurants in Japan are often identified by the food they serve and not who’s serving it. The food is celebrated. The chef? Not so much.
There are exceptions, of course: People in Tokyo, for example, can name their favorite chefs at a range of places, but the standard is the food. And, accordingly, B-grade food costs B-grade prices.