This is the 373rd most frequent Japanese word.
予約
Reservation; appointment.
Here, '予約' is used as a verb ('予約する'), meaning 'to reserve' something like tickets or appointments.
私は映画のチケットを予約しました。
I reserved movie tickets.
In this context, '予約' as a noun is again used to discuss whether prior reservations are required.
このホテルは予約が必要ですか？
Does this hotel require reservations?
Here, '予約' is used as a noun, referring to the act of reserving a spot at a restaurant.