exterior hallway; open-air corridor
Refers to an outdoor hallway, typically along the outside of an apartment building, providing access to individual units. Common in Japanese multi-family housing.
This apartment has an exterior hallway, so you get a little wet on rainy days.
It's a type of apartment building where you enter each unit from an open-air corridor.
Compound of 外 (そと, 'outside') and 廊下 (ろうか, 'corridor').