A Japanese lunch box is called a "bento box" (弁当箱 or べんとうばこ) in Japanese. The word "bento" refers to a single-portion takeout meal or packed lunch that is common in Japanese cuisine. 

Bento boxes are traditionally used to carry and serve these packed meals, which typically consist of a balanced and visually appealing combination of rice, a main dish (such as meat or fish), side dishes (such as vegetables or pickles), and sometimes even a dessert. Bento boxes are popular for their portability, variety, and the cultural significance of providing a well-prepared meal for oneself or loved ones.