noun
single-seat constituency; single-seat electoral district
Used in political contexts to refer to an electoral district that elects only one representative.
この選挙では、一人区の候補者が注目されている。
In this election, the candidates in the single-seat constituencies are attracting attention.
小選挙区 is a broader term for a small electoral district, often synonymous with single-seat constituency, but 一人区 explicitly emphasizes the single-seat aspect.
Compound of 一人 (ひとり, 'one person') and 区 (く, 'ward' or 'district'), literally meaning 'one-person district'.