noun
outside a fort; outside a fortress
General term for the area outside a fortification. Rare in modern standalone use; mostly encountered in historical or literary contexts.
塞外に敵の軍勢が集まっている。
Enemy forces are gathering outside the fort.
noun
outside the Great Wall of China
Specifically refers to the region beyond the Great Wall. A historical term used in classical Chinese and Japanese texts.
塞外の地は、古来より遊牧民の勢力圏だった。
The lands outside the Great Wall have been the sphere of influence of nomadic peoples since ancient times.