A shotgun house is a house that is small and rectangular and has no hallways and usually three rooms. Since the house has no hallways and the doors are always on the same side, it is said that one could fire a shotgun through the front door and the shot would fly cleanly out the back door.
The shotgun house is a narrow rectangular domestic residence, usually no more than 12 feet (3.5 m) wide, with doors at each end. It was the most popular style of house in the Southern United States from the end of theAmerican Civil War (1861–65), through to the 1920s. Alternate names include shotgun shack, shotgun hut, andshotgun cottage. A railroad apartment is somewhat similar, but has a side hallway from which rooms are entered (by analogy to compartments in passenger rail cars).
See the rest of a VERY interesting Wikipedia article about Shotgun Houses here.
In Japan, we don't call them shotgun houses, but we have something like them here. There is one that is near my house. I'll be that, if you stood up in this house and stretched your arms out, you could touch both sides of the wall in any room. I can't imagine how tiny the kitchen and bathroom are.
Here's another photo of a very narrow house in Japan that I found online:
Incredible, but I count four rooms in this home! It's so narrow in there that you don't even have room to change your mind!