noun
eve celebration; pre-event festival; event held the night before
Refers to a celebration, program, or related event held on the night before a main festival, tournament, ceremony, or similar occasion. It can also refer more broadly to the eve of a festival or holiday.
学園祭の前夜祭でバンドが演奏した。
A band performed at the school festival's eve celebration.
大会の前夜祭
All the athletes attended the event held on the night before the tournament.