noun
A former soldier who has returned to civilian life but remains subject to recall. The term is especially associated with pre-war and wartime Japan, though it can be used in modern contexts.
彼は在郷軍人として、年に一度の訓練に参加している。
As a reservist, he participates in annual training.
予備役 refers to the reserve duty or reserve forces as a system, while 在郷軍人 refers to the individual reservist living in the community.
Compound of 在郷 (ざいごう, 'in one's hometown / in the countryside') and 軍人 (ぐんじん, 'military person'). The term arose from the Meiji-era conscription system, where soldiers returned to their hometowns after active service but remained on reserve lists.