Makunouchi bento is a type of bento; boxed meal which has several main dishes and side dishes included together with rice.
Significant differences from other bento are that it is not homemade; must be bought at stores or restaurants, portions of main dishes and side dishes are small and then those dishes are cooked in several ways. Several ways mean deep fried, stewed, grilled and pickled.
Other bento, such as tonkatsu bento includes rice and side dishes such as pickles and salad but only single main dish, deep fried pork cutlet in breadcrumbs = tonkatsu. Although Makunouchi bento can include tonkatsu but extremely smaller portion, usually a single bite of tonkatsu. Therefore Makunouchi bento is recommended to a person who wants to eat several types of dishes at once.
There are several legends why it is called Makunouchi but most likely named after due to eaten at theater. Literally Makunouchi means inside the stage curtain. It can be either eaten by stage actors beyond the stage curtain or by audiences during intermissions.