noun
by-election; special election
An election held to fill a vacant seat between regular elections.
衆議院の補欠選挙が来月行われる。
A by-election for the House of Representatives will be held next month.
総選挙 is a general election for all seats, while 補欠選挙 fills only vacant seats.
Compound of 補欠 (supplementary, filling a vacancy) and 選挙 (election).