expression
all seats reserved; reserved seating only
Used for events, trains, or venues where every seat requires a reservation; no non-reserved seats are available.
この列車は全席指定です。
This train is all reserved seating.
コンサートは全席指定なので、早めに予約してください。
The concert has reserved seats only, so please book early.
自由席 means unreserved or non-reserved seating, where you can sit anywhere in the designated area. 全席指定 means every seat is reserved.
Compound of 全 (all) + 席 (seats) + 指定 (designation/reservation).