As same as restaurants in Europe, many restaurants in Japan also offer lunch menu during weekdays. Then, the menu is not fixed but it is offered as daily offer.
Mostly the offers are not mentioned on websites and therefore customers have to check them on the spot. Then, there are two types of lunch menus. The first type is called Teishoku which main dish comes with rice and miso soup on a single tray called Bon. Teishoku can be also eaten as dinner but not like daily offer. The name of the Teishoku is usually the name of the main dish + teishoku.
The second type is called Set. Set is similar to teishoku but it does not have to be with rice. For example, it can be ramen noodle and gyoza dumplings. Also it is possible to choose the combination, such as ramen noodle and gyoza dumplings, ramen noodle and fried rice or ramen noodle, fried rice and gyoza dumplings. Set can be also available during dinner time too.