There are two dishes that can be translated as "hamburger" in Japan. One is the all-American favorite, a beef patty sandwiched in a bun, which in Japanese is called hanbāgā. The other kind is similar to a Hamburg steak or Salisbury steak, made with chopped onions, breadcrumbs and egg mixed with the ground meat and called hanbāgu. It is pan-fried and served on a plate, often with a rich sauce, and is meant to be eaten with plain steamed rice rather than in a bun.
The distinction between these two dishes is considered so important that the official industry organization for ground meat patty products, the Nihon Hamburg & Hamburger Association, includes both in its name.
The bun-type hamburger has a well-defined history in Japan. Introduced by American GIs after World War II, it became more widely popular in the 1970s and onward with the spread of fast-food franchises such as McDonald's.