This character looks and acts like he/she is from a different country than the VN is set upon. For example if the VN was set in Japan, he/she'd be a gaijin.
Gaijin is a Japanese word meaning "non-Japanese", or "alien". This word is a short form of gaikokujin, which means "foreign country people".
This trait is intended to be used for characters that are clearly foreigners to the game's setting, according to the other characters from the game, but their country of origin is not revealed in any point, or just doesn't exists (anymore) in the real world. Making it not possible to use the other country traits but this.