expression
reservation required; prior booking essential
Fixed phrase used in signs, advertisements, and instructions to indicate that a reservation or booking is mandatory. Often seen in contexts like restaurants, events, and accommodations.
このレストランは要予約です。
This restaurant requires a reservation.
イベント参加は要予約となっております。
Participation in the event requires prior booking.
Compound of 要 (need, require) and 予約 (reservation, booking). The exact historical derivation is uncertain, but it functions as a set phrase in modern Japanese.