Railway bento, or train bento, is a type of bento sold at railroad stations or in train cars. It is called "ekiben" in Japanese. When traveling long distances, i.e. being confined to a train for a long period of time, you may need to eat depending on the time of day you are traveling. That's why there's a trend of selling bento at the station or in the train compartment.

The lunchboxes sold on the platforms inside the stations or on the trains are considered to be lunchboxes if they contain rice as the main food, but in Europe and the United States, it is more ambiguous as to what is considered to be a lunch or dinner. Bread, sandwiches, and snacks are not lunchboxes, so they do not fall into this category.

Expanded Information:

The word "bento" first originated in China during the Southern Song Dynasty in the proverbial "bingdang", which originally meant "something convenient, convenient, smooth". "Bento" (pronounced: bentou) which refers to boxed meals, more has been simplified to translate Bento.

Bento is customarily called "boxed rice" in most parts of the mainland, i.e., boxed meals. In Taiwan, it is generally referred to as a bento, and is usually used for lunch, takeout, and work meals. There is no subtle difference in usage between "bento" and "boxed lunch", only a difference in terminology.

Reference? Baidu Encyclopedia - Railway Bento